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1059 lines
39 KiB
1059 lines
39 KiB
/* SPDX-License-Identifier: GPL-2.0+ */ |
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/* |
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* Read-Copy Update mechanism for mutual exclusion |
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* |
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* Copyright IBM Corporation, 2001 |
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* |
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* Author: Dipankar Sarma <[email protected]> |
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* |
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* Based on the original work by Paul McKenney <[email protected]> |
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* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. |
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* Papers: |
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* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf |
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* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) |
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* |
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* For detailed explanation of Read-Copy Update mechanism see - |
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* http://lse.sourceforge.net/locking/rcupdate.html |
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* |
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*/ |
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#ifndef __LINUX_RCUPDATE_H |
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#define __LINUX_RCUPDATE_H |
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#include <linux/types.h> |
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#include <linux/compiler.h> |
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#include <linux/atomic.h> |
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#include <linux/irqflags.h> |
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#include <linux/preempt.h> |
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#include <linux/bottom_half.h> |
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#include <linux/lockdep.h> |
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#include <asm/processor.h> |
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#include <linux/cpumask.h> |
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#include <linux/context_tracking_irq.h> |
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#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) |
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#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) |
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#define ulong2long(a) (*(long *)(&(a))) |
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#define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b))) |
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#define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b))) |
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/* Exported common interfaces */ |
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void call_rcu(struct rcu_head *head, rcu_callback_t func); |
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void rcu_barrier_tasks(void); |
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void rcu_barrier_tasks_rude(void); |
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void synchronize_rcu(void); |
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struct rcu_gp_oldstate; |
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unsigned long get_completed_synchronize_rcu(void); |
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void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp); |
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// Maximum number of unsigned long values corresponding to |
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// not-yet-completed RCU grace periods. |
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#define NUM_ACTIVE_RCU_POLL_OLDSTATE 2 |
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/** |
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* same_state_synchronize_rcu - Are two old-state values identical? |
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* @oldstate1: First old-state value. |
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* @oldstate2: Second old-state value. |
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* |
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* The two old-state values must have been obtained from either |
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* get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or |
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* get_completed_synchronize_rcu(). Returns @true if the two values are |
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* identical and @false otherwise. This allows structures whose lifetimes |
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* are tracked by old-state values to push these values to a list header, |
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* allowing those structures to be slightly smaller. |
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*/ |
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static inline bool same_state_synchronize_rcu(unsigned long oldstate1, unsigned long oldstate2) |
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{ |
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return oldstate1 == oldstate2; |
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} |
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#ifdef CONFIG_PREEMPT_RCU |
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void __rcu_read_lock(void); |
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void __rcu_read_unlock(void); |
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/* |
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* Defined as a macro as it is a very low level header included from |
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* areas that don't even know about current. This gives the rcu_read_lock() |
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* nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other |
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* types of kernel builds, the rcu_read_lock() nesting depth is unknowable. |
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*/ |
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#define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting) |
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#else /* #ifdef CONFIG_PREEMPT_RCU */ |
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#ifdef CONFIG_TINY_RCU |
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#define rcu_read_unlock_strict() do { } while (0) |
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#else |
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void rcu_read_unlock_strict(void); |
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#endif |
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static inline void __rcu_read_lock(void) |
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{ |
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preempt_disable(); |
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} |
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static inline void __rcu_read_unlock(void) |
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{ |
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preempt_enable(); |
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if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) |
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rcu_read_unlock_strict(); |
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} |
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static inline int rcu_preempt_depth(void) |
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{ |
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return 0; |
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} |
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#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
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/* Internal to kernel */ |
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void rcu_init(void); |
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extern int rcu_scheduler_active; |
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void rcu_sched_clock_irq(int user); |
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void rcu_report_dead(unsigned int cpu); |
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void rcutree_migrate_callbacks(int cpu); |
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#ifdef CONFIG_TASKS_RCU_GENERIC |
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void rcu_init_tasks_generic(void); |
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#else |
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static inline void rcu_init_tasks_generic(void) { } |
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#endif |
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#ifdef CONFIG_RCU_STALL_COMMON |
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void rcu_sysrq_start(void); |
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void rcu_sysrq_end(void); |
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#else /* #ifdef CONFIG_RCU_STALL_COMMON */ |
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static inline void rcu_sysrq_start(void) { } |
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static inline void rcu_sysrq_end(void) { } |
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#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */ |
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#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) |
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void rcu_irq_work_resched(void); |
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#else |
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static inline void rcu_irq_work_resched(void) { } |
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#endif |
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#ifdef CONFIG_RCU_NOCB_CPU |
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void rcu_init_nohz(void); |
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int rcu_nocb_cpu_offload(int cpu); |
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int rcu_nocb_cpu_deoffload(int cpu); |
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void rcu_nocb_flush_deferred_wakeup(void); |
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#else /* #ifdef CONFIG_RCU_NOCB_CPU */ |
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static inline void rcu_init_nohz(void) { } |
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static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; } |
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static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; } |
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static inline void rcu_nocb_flush_deferred_wakeup(void) { } |
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#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ |
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/** |
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* RCU_NONIDLE - Indicate idle-loop code that needs RCU readers |
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* @a: Code that RCU needs to pay attention to. |
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* |
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* RCU read-side critical sections are forbidden in the inner idle loop, |
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* that is, between the ct_idle_enter() and the ct_idle_exit() -- RCU |
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* will happily ignore any such read-side critical sections. However, |
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* things like powertop need tracepoints in the inner idle loop. |
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* |
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* This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) |
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* will tell RCU that it needs to pay attention, invoke its argument |
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* (in this example, calling the do_something_with_RCU() function), |
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* and then tell RCU to go back to ignoring this CPU. It is permissible |
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* to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is |
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* on the order of a million or so, even on 32-bit systems). It is |
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* not legal to block within RCU_NONIDLE(), nor is it permissible to |
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* transfer control either into or out of RCU_NONIDLE()'s statement. |
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*/ |
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#define RCU_NONIDLE(a) \ |
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do { \ |
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ct_irq_enter_irqson(); \ |
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do { a; } while (0); \ |
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ct_irq_exit_irqson(); \ |
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} while (0) |
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/* |
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* Note a quasi-voluntary context switch for RCU-tasks's benefit. |
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* This is a macro rather than an inline function to avoid #include hell. |
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*/ |
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#ifdef CONFIG_TASKS_RCU_GENERIC |
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# ifdef CONFIG_TASKS_RCU |
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# define rcu_tasks_classic_qs(t, preempt) \ |
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do { \ |
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if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \ |
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WRITE_ONCE((t)->rcu_tasks_holdout, false); \ |
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} while (0) |
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void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); |
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void synchronize_rcu_tasks(void); |
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# else |
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# define rcu_tasks_classic_qs(t, preempt) do { } while (0) |
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# define call_rcu_tasks call_rcu |
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# define synchronize_rcu_tasks synchronize_rcu |
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# endif |
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# ifdef CONFIG_TASKS_TRACE_RCU |
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// Bits for ->trc_reader_special.b.need_qs field. |
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#define TRC_NEED_QS 0x1 // Task needs a quiescent state. |
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#define TRC_NEED_QS_CHECKED 0x2 // Task has been checked for needing quiescent state. |
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u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new); |
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void rcu_tasks_trace_qs_blkd(struct task_struct *t); |
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# define rcu_tasks_trace_qs(t) \ |
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do { \ |
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int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting); \ |
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\ |
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if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) && \ |
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likely(!___rttq_nesting)) { \ |
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rcu_trc_cmpxchg_need_qs((t), 0, TRC_NEED_QS_CHECKED); \ |
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} else if (___rttq_nesting && ___rttq_nesting != INT_MIN && \ |
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!READ_ONCE((t)->trc_reader_special.b.blocked)) { \ |
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rcu_tasks_trace_qs_blkd(t); \ |
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} \ |
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} while (0) |
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# else |
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# define rcu_tasks_trace_qs(t) do { } while (0) |
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# endif |
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#define rcu_tasks_qs(t, preempt) \ |
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do { \ |
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rcu_tasks_classic_qs((t), (preempt)); \ |
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rcu_tasks_trace_qs(t); \ |
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} while (0) |
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# ifdef CONFIG_TASKS_RUDE_RCU |
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void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func); |
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void synchronize_rcu_tasks_rude(void); |
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# endif |
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#define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false) |
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void exit_tasks_rcu_start(void); |
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void exit_tasks_rcu_finish(void); |
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#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ |
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#define rcu_tasks_classic_qs(t, preempt) do { } while (0) |
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#define rcu_tasks_qs(t, preempt) do { } while (0) |
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#define rcu_note_voluntary_context_switch(t) do { } while (0) |
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#define call_rcu_tasks call_rcu |
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#define synchronize_rcu_tasks synchronize_rcu |
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static inline void exit_tasks_rcu_start(void) { } |
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static inline void exit_tasks_rcu_finish(void) { } |
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#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ |
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/** |
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* cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU |
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* |
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* This macro resembles cond_resched(), except that it is defined to |
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* report potential quiescent states to RCU-tasks even if the cond_resched() |
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* machinery were to be shut off, as some advocate for PREEMPTION kernels. |
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*/ |
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#define cond_resched_tasks_rcu_qs() \ |
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do { \ |
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rcu_tasks_qs(current, false); \ |
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cond_resched(); \ |
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} while (0) |
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/* |
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* Infrastructure to implement the synchronize_() primitives in |
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* TREE_RCU and rcu_barrier_() primitives in TINY_RCU. |
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*/ |
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#if defined(CONFIG_TREE_RCU) |
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#include <linux/rcutree.h> |
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#elif defined(CONFIG_TINY_RCU) |
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#include <linux/rcutiny.h> |
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#else |
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#error "Unknown RCU implementation specified to kernel configuration" |
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#endif |
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/* |
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* The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls |
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* are needed for dynamic initialization and destruction of rcu_head |
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* on the stack, and init_rcu_head()/destroy_rcu_head() are needed for |
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* dynamic initialization and destruction of statically allocated rcu_head |
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* structures. However, rcu_head structures allocated dynamically in the |
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* heap don't need any initialization. |
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*/ |
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#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD |
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void init_rcu_head(struct rcu_head *head); |
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void destroy_rcu_head(struct rcu_head *head); |
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void init_rcu_head_on_stack(struct rcu_head *head); |
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void destroy_rcu_head_on_stack(struct rcu_head *head); |
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#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
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static inline void init_rcu_head(struct rcu_head *head) { } |
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static inline void destroy_rcu_head(struct rcu_head *head) { } |
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static inline void init_rcu_head_on_stack(struct rcu_head *head) { } |
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static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { } |
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#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
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#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) |
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bool rcu_lockdep_current_cpu_online(void); |
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#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ |
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static inline bool rcu_lockdep_current_cpu_online(void) { return true; } |
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#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ |
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extern struct lockdep_map rcu_lock_map; |
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extern struct lockdep_map rcu_bh_lock_map; |
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extern struct lockdep_map rcu_sched_lock_map; |
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extern struct lockdep_map rcu_callback_map; |
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#ifdef CONFIG_DEBUG_LOCK_ALLOC |
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static inline void rcu_lock_acquire(struct lockdep_map *map) |
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{ |
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lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); |
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} |
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static inline void rcu_lock_release(struct lockdep_map *map) |
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{ |
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lock_release(map, _THIS_IP_); |
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} |
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int debug_lockdep_rcu_enabled(void); |
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int rcu_read_lock_held(void); |
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int rcu_read_lock_bh_held(void); |
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int rcu_read_lock_sched_held(void); |
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int rcu_read_lock_any_held(void); |
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#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
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# define rcu_lock_acquire(a) do { } while (0) |
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# define rcu_lock_release(a) do { } while (0) |
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static inline int rcu_read_lock_held(void) |
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{ |
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return 1; |
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} |
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static inline int rcu_read_lock_bh_held(void) |
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{ |
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return 1; |
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} |
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static inline int rcu_read_lock_sched_held(void) |
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{ |
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return !preemptible(); |
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} |
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static inline int rcu_read_lock_any_held(void) |
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{ |
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return !preemptible(); |
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} |
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#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
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#ifdef CONFIG_PROVE_RCU |
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/** |
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* RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met |
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* @c: condition to check |
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* @s: informative message |
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*/ |
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#define RCU_LOCKDEP_WARN(c, s) \ |
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do { \ |
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static bool __section(".data.unlikely") __warned; \ |
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if ((c) && debug_lockdep_rcu_enabled() && !__warned) { \ |
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__warned = true; \ |
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lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ |
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} \ |
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} while (0) |
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#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) |
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static inline void rcu_preempt_sleep_check(void) |
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{ |
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RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map), |
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"Illegal context switch in RCU read-side critical section"); |
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} |
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#else /* #ifdef CONFIG_PROVE_RCU */ |
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static inline void rcu_preempt_sleep_check(void) { } |
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#endif /* #else #ifdef CONFIG_PROVE_RCU */ |
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#define rcu_sleep_check() \ |
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do { \ |
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rcu_preempt_sleep_check(); \ |
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if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \ |
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RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \ |
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"Illegal context switch in RCU-bh read-side critical section"); \ |
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RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \ |
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"Illegal context switch in RCU-sched read-side critical section"); \ |
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} while (0) |
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#else /* #ifdef CONFIG_PROVE_RCU */ |
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#define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c)) |
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#define rcu_sleep_check() do { } while (0) |
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#endif /* #else #ifdef CONFIG_PROVE_RCU */ |
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/* |
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* Helper functions for rcu_dereference_check(), rcu_dereference_protected() |
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* and rcu_assign_pointer(). Some of these could be folded into their |
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* callers, but they are left separate in order to ease introduction of |
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* multiple pointers markings to match different RCU implementations |
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* (e.g., __srcu), should this make sense in the future. |
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*/ |
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#ifdef __CHECKER__ |
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#define rcu_check_sparse(p, space) \ |
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((void)(((typeof(*p) space *)p) == p)) |
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#else /* #ifdef __CHECKER__ */ |
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#define rcu_check_sparse(p, space) |
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#endif /* #else #ifdef __CHECKER__ */ |
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#define __unrcu_pointer(p, local) \ |
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({ \ |
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typeof(*p) *local = (typeof(*p) *__force)(p); \ |
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rcu_check_sparse(p, __rcu); \ |
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((typeof(*p) __force __kernel *)(local)); \ |
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}) |
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/** |
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* unrcu_pointer - mark a pointer as not being RCU protected |
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* @p: pointer needing to lose its __rcu property |
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* |
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* Converts @p from an __rcu pointer to a __kernel pointer. |
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* This allows an __rcu pointer to be used with xchg() and friends. |
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*/ |
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#define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu)) |
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#define __rcu_access_pointer(p, local, space) \ |
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({ \ |
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typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ |
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rcu_check_sparse(p, space); \ |
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((typeof(*p) __force __kernel *)(local)); \ |
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}) |
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#define __rcu_dereference_check(p, local, c, space) \ |
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({ \ |
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/* Dependency order vs. p above. */ \ |
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typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ |
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RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ |
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rcu_check_sparse(p, space); \ |
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((typeof(*p) __force __kernel *)(local)); \ |
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}) |
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#define __rcu_dereference_protected(p, local, c, space) \ |
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({ \ |
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RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ |
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rcu_check_sparse(p, space); \ |
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((typeof(*p) __force __kernel *)(p)); \ |
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}) |
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#define __rcu_dereference_raw(p, local) \ |
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({ \ |
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/* Dependency order vs. p above. */ \ |
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typeof(p) local = READ_ONCE(p); \ |
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((typeof(*p) __force __kernel *)(local)); \ |
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}) |
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#define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu)) |
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/** |
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* RCU_INITIALIZER() - statically initialize an RCU-protected global variable |
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* @v: The value to statically initialize with. |
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*/ |
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#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) |
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/** |
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* rcu_assign_pointer() - assign to RCU-protected pointer |
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* @p: pointer to assign to |
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* @v: value to assign (publish) |
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* |
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* Assigns the specified value to the specified RCU-protected |
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* pointer, ensuring that any concurrent RCU readers will see |
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* any prior initialization. |
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* |
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* Inserts memory barriers on architectures that require them |
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* (which is most of them), and also prevents the compiler from |
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* reordering the code that initializes the structure after the pointer |
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* assignment. More importantly, this call documents which pointers |
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* will be dereferenced by RCU read-side code. |
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* |
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* In some special cases, you may use RCU_INIT_POINTER() instead |
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* of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due |
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* to the fact that it does not constrain either the CPU or the compiler. |
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* That said, using RCU_INIT_POINTER() when you should have used |
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* rcu_assign_pointer() is a very bad thing that results in |
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* impossible-to-diagnose memory corruption. So please be careful. |
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* See the RCU_INIT_POINTER() comment header for details. |
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* |
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* Note that rcu_assign_pointer() evaluates each of its arguments only |
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* once, appearances notwithstanding. One of the "extra" evaluations |
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* is in typeof() and the other visible only to sparse (__CHECKER__), |
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* neither of which actually execute the argument. As with most cpp |
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* macros, this execute-arguments-only-once property is important, so |
|
* please be careful when making changes to rcu_assign_pointer() and the |
|
* other macros that it invokes. |
|
*/ |
|
#define rcu_assign_pointer(p, v) \ |
|
do { \ |
|
uintptr_t _r_a_p__v = (uintptr_t)(v); \ |
|
rcu_check_sparse(p, __rcu); \ |
|
\ |
|
if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \ |
|
WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ |
|
else \ |
|
smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ |
|
} while (0) |
|
|
|
/** |
|
* rcu_replace_pointer() - replace an RCU pointer, returning its old value |
|
* @rcu_ptr: RCU pointer, whose old value is returned |
|
* @ptr: regular pointer |
|
* @c: the lockdep conditions under which the dereference will take place |
|
* |
|
* Perform a replacement, where @rcu_ptr is an RCU-annotated |
|
* pointer and @c is the lockdep argument that is passed to the |
|
* rcu_dereference_protected() call used to read that pointer. The old |
|
* value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr. |
|
*/ |
|
#define rcu_replace_pointer(rcu_ptr, ptr, c) \ |
|
({ \ |
|
typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ |
|
rcu_assign_pointer((rcu_ptr), (ptr)); \ |
|
__tmp; \ |
|
}) |
|
|
|
/** |
|
* rcu_access_pointer() - fetch RCU pointer with no dereferencing |
|
* @p: The pointer to read |
|
* |
|
* Return the value of the specified RCU-protected pointer, but omit the |
|
* lockdep checks for being in an RCU read-side critical section. This is |
|
* useful when the value of this pointer is accessed, but the pointer is |
|
* not dereferenced, for example, when testing an RCU-protected pointer |
|
* against NULL. Although rcu_access_pointer() may also be used in cases |
|
* where update-side locks prevent the value of the pointer from changing, |
|
* you should instead use rcu_dereference_protected() for this use case. |
|
* Within an RCU read-side critical section, there is little reason to |
|
* use rcu_access_pointer(). |
|
* |
|
* It is usually best to test the rcu_access_pointer() return value |
|
* directly in order to avoid accidental dereferences being introduced |
|
* by later inattentive changes. In other words, assigning the |
|
* rcu_access_pointer() return value to a local variable results in an |
|
* accident waiting to happen. |
|
* |
|
* It is also permissible to use rcu_access_pointer() when read-side |
|
* access to the pointer was removed at least one grace period ago, as is |
|
* the case in the context of the RCU callback that is freeing up the data, |
|
* or after a synchronize_rcu() returns. This can be useful when tearing |
|
* down multi-linked structures after a grace period has elapsed. However, |
|
* rcu_dereference_protected() is normally preferred for this use case. |
|
*/ |
|
#define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu) |
|
|
|
/** |
|
* rcu_dereference_check() - rcu_dereference with debug checking |
|
* @p: The pointer to read, prior to dereferencing |
|
* @c: The conditions under which the dereference will take place |
|
* |
|
* Do an rcu_dereference(), but check that the conditions under which the |
|
* dereference will take place are correct. Typically the conditions |
|
* indicate the various locking conditions that should be held at that |
|
* point. The check should return true if the conditions are satisfied. |
|
* An implicit check for being in an RCU read-side critical section |
|
* (rcu_read_lock()) is included. |
|
* |
|
* For example: |
|
* |
|
* bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
|
* |
|
* could be used to indicate to lockdep that foo->bar may only be dereferenced |
|
* if either rcu_read_lock() is held, or that the lock required to replace |
|
* the bar struct at foo->bar is held. |
|
* |
|
* Note that the list of conditions may also include indications of when a lock |
|
* need not be held, for example during initialisation or destruction of the |
|
* target struct: |
|
* |
|
* bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
|
* atomic_read(&foo->usage) == 0); |
|
* |
|
* Inserts memory barriers on architectures that require them |
|
* (currently only the Alpha), prevents the compiler from refetching |
|
* (and from merging fetches), and, more importantly, documents exactly |
|
* which pointers are protected by RCU and checks that the pointer is |
|
* annotated as __rcu. |
|
*/ |
|
#define rcu_dereference_check(p, c) \ |
|
__rcu_dereference_check((p), __UNIQUE_ID(rcu), \ |
|
(c) || rcu_read_lock_held(), __rcu) |
|
|
|
/** |
|
* rcu_dereference_bh_check() - rcu_dereference_bh with debug checking |
|
* @p: The pointer to read, prior to dereferencing |
|
* @c: The conditions under which the dereference will take place |
|
* |
|
* This is the RCU-bh counterpart to rcu_dereference_check(). However, |
|
* please note that starting in v5.0 kernels, vanilla RCU grace periods |
|
* wait for local_bh_disable() regions of code in addition to regions of |
|
* code demarked by rcu_read_lock() and rcu_read_unlock(). This means |
|
* that synchronize_rcu(), call_rcu, and friends all take not only |
|
* rcu_read_lock() but also rcu_read_lock_bh() into account. |
|
*/ |
|
#define rcu_dereference_bh_check(p, c) \ |
|
__rcu_dereference_check((p), __UNIQUE_ID(rcu), \ |
|
(c) || rcu_read_lock_bh_held(), __rcu) |
|
|
|
/** |
|
* rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
|
* @p: The pointer to read, prior to dereferencing |
|
* @c: The conditions under which the dereference will take place |
|
* |
|
* This is the RCU-sched counterpart to rcu_dereference_check(). |
|
* However, please note that starting in v5.0 kernels, vanilla RCU grace |
|
* periods wait for preempt_disable() regions of code in addition to |
|
* regions of code demarked by rcu_read_lock() and rcu_read_unlock(). |
|
* This means that synchronize_rcu(), call_rcu, and friends all take not |
|
* only rcu_read_lock() but also rcu_read_lock_sched() into account. |
|
*/ |
|
#define rcu_dereference_sched_check(p, c) \ |
|
__rcu_dereference_check((p), __UNIQUE_ID(rcu), \ |
|
(c) || rcu_read_lock_sched_held(), \ |
|
__rcu) |
|
|
|
/* |
|
* The tracing infrastructure traces RCU (we want that), but unfortunately |
|
* some of the RCU checks causes tracing to lock up the system. |
|
* |
|
* The no-tracing version of rcu_dereference_raw() must not call |
|
* rcu_read_lock_held(). |
|
*/ |
|
#define rcu_dereference_raw_check(p) \ |
|
__rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu) |
|
|
|
/** |
|
* rcu_dereference_protected() - fetch RCU pointer when updates prevented |
|
* @p: The pointer to read, prior to dereferencing |
|
* @c: The conditions under which the dereference will take place |
|
* |
|
* Return the value of the specified RCU-protected pointer, but omit |
|
* the READ_ONCE(). This is useful in cases where update-side locks |
|
* prevent the value of the pointer from changing. Please note that this |
|
* primitive does *not* prevent the compiler from repeating this reference |
|
* or combining it with other references, so it should not be used without |
|
* protection of appropriate locks. |
|
* |
|
* This function is only for update-side use. Using this function |
|
* when protected only by rcu_read_lock() will result in infrequent |
|
* but very ugly failures. |
|
*/ |
|
#define rcu_dereference_protected(p, c) \ |
|
__rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu) |
|
|
|
|
|
/** |
|
* rcu_dereference() - fetch RCU-protected pointer for dereferencing |
|
* @p: The pointer to read, prior to dereferencing |
|
* |
|
* This is a simple wrapper around rcu_dereference_check(). |
|
*/ |
|
#define rcu_dereference(p) rcu_dereference_check(p, 0) |
|
|
|
/** |
|
* rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
|
* @p: The pointer to read, prior to dereferencing |
|
* |
|
* Makes rcu_dereference_check() do the dirty work. |
|
*/ |
|
#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) |
|
|
|
/** |
|
* rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing |
|
* @p: The pointer to read, prior to dereferencing |
|
* |
|
* Makes rcu_dereference_check() do the dirty work. |
|
*/ |
|
#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) |
|
|
|
/** |
|
* rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism |
|
* @p: The pointer to hand off |
|
* |
|
* This is simply an identity function, but it documents where a pointer |
|
* is handed off from RCU to some other synchronization mechanism, for |
|
* example, reference counting or locking. In C11, it would map to |
|
* kill_dependency(). It could be used as follows:: |
|
* |
|
* rcu_read_lock(); |
|
* p = rcu_dereference(gp); |
|
* long_lived = is_long_lived(p); |
|
* if (long_lived) { |
|
* if (!atomic_inc_not_zero(p->refcnt)) |
|
* long_lived = false; |
|
* else |
|
* p = rcu_pointer_handoff(p); |
|
* } |
|
* rcu_read_unlock(); |
|
*/ |
|
#define rcu_pointer_handoff(p) (p) |
|
|
|
/** |
|
* rcu_read_lock() - mark the beginning of an RCU read-side critical section |
|
* |
|
* When synchronize_rcu() is invoked on one CPU while other CPUs |
|
* are within RCU read-side critical sections, then the |
|
* synchronize_rcu() is guaranteed to block until after all the other |
|
* CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
|
* on one CPU while other CPUs are within RCU read-side critical |
|
* sections, invocation of the corresponding RCU callback is deferred |
|
* until after the all the other CPUs exit their critical sections. |
|
* |
|
* In v5.0 and later kernels, synchronize_rcu() and call_rcu() also |
|
* wait for regions of code with preemption disabled, including regions of |
|
* code with interrupts or softirqs disabled. In pre-v5.0 kernels, which |
|
* define synchronize_sched(), only code enclosed within rcu_read_lock() |
|
* and rcu_read_unlock() are guaranteed to be waited for. |
|
* |
|
* Note, however, that RCU callbacks are permitted to run concurrently |
|
* with new RCU read-side critical sections. One way that this can happen |
|
* is via the following sequence of events: (1) CPU 0 enters an RCU |
|
* read-side critical section, (2) CPU 1 invokes call_rcu() to register |
|
* an RCU callback, (3) CPU 0 exits the RCU read-side critical section, |
|
* (4) CPU 2 enters a RCU read-side critical section, (5) the RCU |
|
* callback is invoked. This is legal, because the RCU read-side critical |
|
* section that was running concurrently with the call_rcu() (and which |
|
* therefore might be referencing something that the corresponding RCU |
|
* callback would free up) has completed before the corresponding |
|
* RCU callback is invoked. |
|
* |
|
* RCU read-side critical sections may be nested. Any deferred actions |
|
* will be deferred until the outermost RCU read-side critical section |
|
* completes. |
|
* |
|
* You can avoid reading and understanding the next paragraph by |
|
* following this rule: don't put anything in an rcu_read_lock() RCU |
|
* read-side critical section that would block in a !PREEMPTION kernel. |
|
* But if you want the full story, read on! |
|
* |
|
* In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU), |
|
* it is illegal to block while in an RCU read-side critical section. |
|
* In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION |
|
* kernel builds, RCU read-side critical sections may be preempted, |
|
* but explicit blocking is illegal. Finally, in preemptible RCU |
|
* implementations in real-time (with -rt patchset) kernel builds, RCU |
|
* read-side critical sections may be preempted and they may also block, but |
|
* only when acquiring spinlocks that are subject to priority inheritance. |
|
*/ |
|
static __always_inline void rcu_read_lock(void) |
|
{ |
|
__rcu_read_lock(); |
|
__acquire(RCU); |
|
rcu_lock_acquire(&rcu_lock_map); |
|
RCU_LOCKDEP_WARN(!rcu_is_watching(), |
|
"rcu_read_lock() used illegally while idle"); |
|
} |
|
|
|
/* |
|
* So where is rcu_write_lock()? It does not exist, as there is no |
|
* way for writers to lock out RCU readers. This is a feature, not |
|
* a bug -- this property is what provides RCU's performance benefits. |
|
* Of course, writers must coordinate with each other. The normal |
|
* spinlock primitives work well for this, but any other technique may be |
|
* used as well. RCU does not care how the writers keep out of each |
|
* others' way, as long as they do so. |
|
*/ |
|
|
|
/** |
|
* rcu_read_unlock() - marks the end of an RCU read-side critical section. |
|
* |
|
* In almost all situations, rcu_read_unlock() is immune from deadlock. |
|
* In recent kernels that have consolidated synchronize_sched() and |
|
* synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity |
|
* also extends to the scheduler's runqueue and priority-inheritance |
|
* spinlocks, courtesy of the quiescent-state deferral that is carried |
|
* out when rcu_read_unlock() is invoked with interrupts disabled. |
|
* |
|
* See rcu_read_lock() for more information. |
|
*/ |
|
static inline void rcu_read_unlock(void) |
|
{ |
|
RCU_LOCKDEP_WARN(!rcu_is_watching(), |
|
"rcu_read_unlock() used illegally while idle"); |
|
__release(RCU); |
|
__rcu_read_unlock(); |
|
rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ |
|
} |
|
|
|
/** |
|
* rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
|
* |
|
* This is equivalent to rcu_read_lock(), but also disables softirqs. |
|
* Note that anything else that disables softirqs can also serve as an RCU |
|
* read-side critical section. However, please note that this equivalence |
|
* applies only to v5.0 and later. Before v5.0, rcu_read_lock() and |
|
* rcu_read_lock_bh() were unrelated. |
|
* |
|
* Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() |
|
* must occur in the same context, for example, it is illegal to invoke |
|
* rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() |
|
* was invoked from some other task. |
|
*/ |
|
static inline void rcu_read_lock_bh(void) |
|
{ |
|
local_bh_disable(); |
|
__acquire(RCU_BH); |
|
rcu_lock_acquire(&rcu_bh_lock_map); |
|
RCU_LOCKDEP_WARN(!rcu_is_watching(), |
|
"rcu_read_lock_bh() used illegally while idle"); |
|
} |
|
|
|
/** |
|
* rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section |
|
* |
|
* See rcu_read_lock_bh() for more information. |
|
*/ |
|
static inline void rcu_read_unlock_bh(void) |
|
{ |
|
RCU_LOCKDEP_WARN(!rcu_is_watching(), |
|
"rcu_read_unlock_bh() used illegally while idle"); |
|
rcu_lock_release(&rcu_bh_lock_map); |
|
__release(RCU_BH); |
|
local_bh_enable(); |
|
} |
|
|
|
/** |
|
* rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
|
* |
|
* This is equivalent to rcu_read_lock(), but also disables preemption. |
|
* Read-side critical sections can also be introduced by anything else that |
|
* disables preemption, including local_irq_disable() and friends. However, |
|
* please note that the equivalence to rcu_read_lock() applies only to |
|
* v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched() |
|
* were unrelated. |
|
* |
|
* Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() |
|
* must occur in the same context, for example, it is illegal to invoke |
|
* rcu_read_unlock_sched() from process context if the matching |
|
* rcu_read_lock_sched() was invoked from an NMI handler. |
|
*/ |
|
static inline void rcu_read_lock_sched(void) |
|
{ |
|
preempt_disable(); |
|
__acquire(RCU_SCHED); |
|
rcu_lock_acquire(&rcu_sched_lock_map); |
|
RCU_LOCKDEP_WARN(!rcu_is_watching(), |
|
"rcu_read_lock_sched() used illegally while idle"); |
|
} |
|
|
|
/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
|
static inline notrace void rcu_read_lock_sched_notrace(void) |
|
{ |
|
preempt_disable_notrace(); |
|
__acquire(RCU_SCHED); |
|
} |
|
|
|
/** |
|
* rcu_read_unlock_sched() - marks the end of a RCU-classic critical section |
|
* |
|
* See rcu_read_lock_sched() for more information. |
|
*/ |
|
static inline void rcu_read_unlock_sched(void) |
|
{ |
|
RCU_LOCKDEP_WARN(!rcu_is_watching(), |
|
"rcu_read_unlock_sched() used illegally while idle"); |
|
rcu_lock_release(&rcu_sched_lock_map); |
|
__release(RCU_SCHED); |
|
preempt_enable(); |
|
} |
|
|
|
/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
|
static inline notrace void rcu_read_unlock_sched_notrace(void) |
|
{ |
|
__release(RCU_SCHED); |
|
preempt_enable_notrace(); |
|
} |
|
|
|
/** |
|
* RCU_INIT_POINTER() - initialize an RCU protected pointer |
|
* @p: The pointer to be initialized. |
|
* @v: The value to initialized the pointer to. |
|
* |
|
* Initialize an RCU-protected pointer in special cases where readers |
|
* do not need ordering constraints on the CPU or the compiler. These |
|
* special cases are: |
|
* |
|
* 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or* |
|
* 2. The caller has taken whatever steps are required to prevent |
|
* RCU readers from concurrently accessing this pointer *or* |
|
* 3. The referenced data structure has already been exposed to |
|
* readers either at compile time or via rcu_assign_pointer() *and* |
|
* |
|
* a. You have not made *any* reader-visible changes to |
|
* this structure since then *or* |
|
* b. It is OK for readers accessing this structure from its |
|
* new location to see the old state of the structure. (For |
|
* example, the changes were to statistical counters or to |
|
* other state where exact synchronization is not required.) |
|
* |
|
* Failure to follow these rules governing use of RCU_INIT_POINTER() will |
|
* result in impossible-to-diagnose memory corruption. As in the structures |
|
* will look OK in crash dumps, but any concurrent RCU readers might |
|
* see pre-initialized values of the referenced data structure. So |
|
* please be very careful how you use RCU_INIT_POINTER()!!! |
|
* |
|
* If you are creating an RCU-protected linked structure that is accessed |
|
* by a single external-to-structure RCU-protected pointer, then you may |
|
* use RCU_INIT_POINTER() to initialize the internal RCU-protected |
|
* pointers, but you must use rcu_assign_pointer() to initialize the |
|
* external-to-structure pointer *after* you have completely initialized |
|
* the reader-accessible portions of the linked structure. |
|
* |
|
* Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no |
|
* ordering guarantees for either the CPU or the compiler. |
|
*/ |
|
#define RCU_INIT_POINTER(p, v) \ |
|
do { \ |
|
rcu_check_sparse(p, __rcu); \ |
|
WRITE_ONCE(p, RCU_INITIALIZER(v)); \ |
|
} while (0) |
|
|
|
/** |
|
* RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer |
|
* @p: The pointer to be initialized. |
|
* @v: The value to initialized the pointer to. |
|
* |
|
* GCC-style initialization for an RCU-protected pointer in a structure field. |
|
*/ |
|
#define RCU_POINTER_INITIALIZER(p, v) \ |
|
.p = RCU_INITIALIZER(v) |
|
|
|
/* |
|
* Does the specified offset indicate that the corresponding rcu_head |
|
* structure can be handled by kvfree_rcu()? |
|
*/ |
|
#define __is_kvfree_rcu_offset(offset) ((offset) < 4096) |
|
|
|
/** |
|
* kfree_rcu() - kfree an object after a grace period. |
|
* @ptr: pointer to kfree for both single- and double-argument invocations. |
|
* @rhf: the name of the struct rcu_head within the type of @ptr, |
|
* but only for double-argument invocations. |
|
* |
|
* Many rcu callbacks functions just call kfree() on the base structure. |
|
* These functions are trivial, but their size adds up, and furthermore |
|
* when they are used in a kernel module, that module must invoke the |
|
* high-latency rcu_barrier() function at module-unload time. |
|
* |
|
* The kfree_rcu() function handles this issue. Rather than encoding a |
|
* function address in the embedded rcu_head structure, kfree_rcu() instead |
|
* encodes the offset of the rcu_head structure within the base structure. |
|
* Because the functions are not allowed in the low-order 4096 bytes of |
|
* kernel virtual memory, offsets up to 4095 bytes can be accommodated. |
|
* If the offset is larger than 4095 bytes, a compile-time error will |
|
* be generated in kvfree_rcu_arg_2(). If this error is triggered, you can |
|
* either fall back to use of call_rcu() or rearrange the structure to |
|
* position the rcu_head structure into the first 4096 bytes. |
|
* |
|
* Note that the allowable offset might decrease in the future, for example, |
|
* to allow something like kmem_cache_free_rcu(). |
|
* |
|
* The BUILD_BUG_ON check must not involve any function calls, hence the |
|
* checks are done in macros here. |
|
*/ |
|
#define kfree_rcu(ptr, rhf...) kvfree_rcu(ptr, ## rhf) |
|
|
|
/** |
|
* kvfree_rcu() - kvfree an object after a grace period. |
|
* |
|
* This macro consists of one or two arguments and it is |
|
* based on whether an object is head-less or not. If it |
|
* has a head then a semantic stays the same as it used |
|
* to be before: |
|
* |
|
* kvfree_rcu(ptr, rhf); |
|
* |
|
* where @ptr is a pointer to kvfree(), @rhf is the name |
|
* of the rcu_head structure within the type of @ptr. |
|
* |
|
* When it comes to head-less variant, only one argument |
|
* is passed and that is just a pointer which has to be |
|
* freed after a grace period. Therefore the semantic is |
|
* |
|
* kvfree_rcu(ptr); |
|
* |
|
* where @ptr is the pointer to be freed by kvfree(). |
|
* |
|
* Please note, head-less way of freeing is permitted to |
|
* use from a context that has to follow might_sleep() |
|
* annotation. Otherwise, please switch and embed the |
|
* rcu_head structure within the type of @ptr. |
|
*/ |
|
#define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__, \ |
|
kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__) |
|
|
|
#define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME |
|
#define kvfree_rcu_arg_2(ptr, rhf) \ |
|
do { \ |
|
typeof (ptr) ___p = (ptr); \ |
|
\ |
|
if (___p) { \ |
|
BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf))); \ |
|
kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long) \ |
|
(offsetof(typeof(*(ptr)), rhf))); \ |
|
} \ |
|
} while (0) |
|
|
|
#define kvfree_rcu_arg_1(ptr) \ |
|
do { \ |
|
typeof(ptr) ___p = (ptr); \ |
|
\ |
|
if (___p) \ |
|
kvfree_call_rcu(NULL, (rcu_callback_t) (___p)); \ |
|
} while (0) |
|
|
|
/* |
|
* Place this after a lock-acquisition primitive to guarantee that |
|
* an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies |
|
* if the UNLOCK and LOCK are executed by the same CPU or if the |
|
* UNLOCK and LOCK operate on the same lock variable. |
|
*/ |
|
#ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE |
|
#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ |
|
#else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
|
#define smp_mb__after_unlock_lock() do { } while (0) |
|
#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
|
|
|
|
|
/* Has the specified rcu_head structure been handed to call_rcu()? */ |
|
|
|
/** |
|
* rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu() |
|
* @rhp: The rcu_head structure to initialize. |
|
* |
|
* If you intend to invoke rcu_head_after_call_rcu() to test whether a |
|
* given rcu_head structure has already been passed to call_rcu(), then |
|
* you must also invoke this rcu_head_init() function on it just after |
|
* allocating that structure. Calls to this function must not race with |
|
* calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation. |
|
*/ |
|
static inline void rcu_head_init(struct rcu_head *rhp) |
|
{ |
|
rhp->func = (rcu_callback_t)~0L; |
|
} |
|
|
|
/** |
|
* rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()? |
|
* @rhp: The rcu_head structure to test. |
|
* @f: The function passed to call_rcu() along with @rhp. |
|
* |
|
* Returns @true if the @rhp has been passed to call_rcu() with @func, |
|
* and @false otherwise. Emits a warning in any other case, including |
|
* the case where @rhp has already been invoked after a grace period. |
|
* Calls to this function must not race with callback invocation. One way |
|
* to avoid such races is to enclose the call to rcu_head_after_call_rcu() |
|
* in an RCU read-side critical section that includes a read-side fetch |
|
* of the pointer to the structure containing @rhp. |
|
*/ |
|
static inline bool |
|
rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) |
|
{ |
|
rcu_callback_t func = READ_ONCE(rhp->func); |
|
|
|
if (func == f) |
|
return true; |
|
WARN_ON_ONCE(func != (rcu_callback_t)~0L); |
|
return false; |
|
} |
|
|
|
/* kernel/ksysfs.c definitions */ |
|
extern int rcu_expedited; |
|
extern int rcu_normal; |
|
|
|
#endif /* __LINUX_RCUPDATE_H */
|
|
|