mirror of https://github.com/Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
920 lines
28 KiB
920 lines
28 KiB
/* |
|
* Read-Copy Update mechanism for mutual exclusion |
|
* |
|
* This program is free software; you can redistribute it and/or modify |
|
* it under the terms of the GNU General Public License as published by |
|
* the Free Software Foundation; either version 2 of the License, or |
|
* (at your option) any later version. |
|
* |
|
* This program is distributed in the hope that it will be useful, |
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of |
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
|
* GNU General Public License for more details. |
|
* |
|
* You should have received a copy of the GNU General Public License |
|
* along with this program; if not, you can access it online at |
|
* http://www.gnu.org/licenses/gpl-2.0.html. |
|
* |
|
* Copyright IBM Corporation, 2001 |
|
* |
|
* Authors: Dipankar Sarma <[email protected]> |
|
* Manfred Spraul <[email protected]> |
|
* |
|
* Based on the original work by Paul McKenney <[email protected]> |
|
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. |
|
* Papers: |
|
* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf |
|
* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) |
|
* |
|
* For detailed explanation of Read-Copy Update mechanism see - |
|
* http://lse.sourceforge.net/locking/rcupdate.html |
|
* |
|
*/ |
|
#include <linux/types.h> |
|
#include <linux/kernel.h> |
|
#include <linux/init.h> |
|
#include <linux/spinlock.h> |
|
#include <linux/smp.h> |
|
#include <linux/interrupt.h> |
|
#include <linux/sched.h> |
|
#include <linux/atomic.h> |
|
#include <linux/bitops.h> |
|
#include <linux/percpu.h> |
|
#include <linux/notifier.h> |
|
#include <linux/cpu.h> |
|
#include <linux/mutex.h> |
|
#include <linux/export.h> |
|
#include <linux/hardirq.h> |
|
#include <linux/delay.h> |
|
#include <linux/moduleparam.h> |
|
#include <linux/kthread.h> |
|
#include <linux/tick.h> |
|
|
|
#define CREATE_TRACE_POINTS |
|
|
|
#include "rcu.h" |
|
|
|
#ifdef MODULE_PARAM_PREFIX |
|
#undef MODULE_PARAM_PREFIX |
|
#endif |
|
#define MODULE_PARAM_PREFIX "rcupdate." |
|
|
|
#ifndef CONFIG_TINY_RCU |
|
module_param(rcu_expedited, int, 0); |
|
module_param(rcu_normal, int, 0); |
|
static int rcu_normal_after_boot; |
|
module_param(rcu_normal_after_boot, int, 0); |
|
#endif /* #ifndef CONFIG_TINY_RCU */ |
|
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC |
|
/** |
|
* rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? |
|
* |
|
* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an |
|
* RCU-sched read-side critical section. In absence of |
|
* CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side |
|
* critical section unless it can prove otherwise. Note that disabling |
|
* of preemption (including disabling irqs) counts as an RCU-sched |
|
* read-side critical section. This is useful for debug checks in functions |
|
* that required that they be called within an RCU-sched read-side |
|
* critical section. |
|
* |
|
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot |
|
* and while lockdep is disabled. |
|
* |
|
* Note that if the CPU is in the idle loop from an RCU point of |
|
* view (ie: that we are in the section between rcu_idle_enter() and |
|
* rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU |
|
* did an rcu_read_lock(). The reason for this is that RCU ignores CPUs |
|
* that are in such a section, considering these as in extended quiescent |
|
* state, so such a CPU is effectively never in an RCU read-side critical |
|
* section regardless of what RCU primitives it invokes. This state of |
|
* affairs is required --- we need to keep an RCU-free window in idle |
|
* where the CPU may possibly enter into low power mode. This way we can |
|
* notice an extended quiescent state to other CPUs that started a grace |
|
* period. Otherwise we would delay any grace period as long as we run in |
|
* the idle task. |
|
* |
|
* Similarly, we avoid claiming an SRCU read lock held if the current |
|
* CPU is offline. |
|
*/ |
|
int rcu_read_lock_sched_held(void) |
|
{ |
|
int lockdep_opinion = 0; |
|
|
|
if (!debug_lockdep_rcu_enabled()) |
|
return 1; |
|
if (!rcu_is_watching()) |
|
return 0; |
|
if (!rcu_lockdep_current_cpu_online()) |
|
return 0; |
|
if (debug_locks) |
|
lockdep_opinion = lock_is_held(&rcu_sched_lock_map); |
|
return lockdep_opinion || !preemptible(); |
|
} |
|
EXPORT_SYMBOL(rcu_read_lock_sched_held); |
|
#endif |
|
|
|
#ifndef CONFIG_TINY_RCU |
|
|
|
/* |
|
* Should expedited grace-period primitives always fall back to their |
|
* non-expedited counterparts? Intended for use within RCU. Note |
|
* that if the user specifies both rcu_expedited and rcu_normal, then |
|
* rcu_normal wins. (Except during the time period during boot from |
|
* when the first task is spawned until the rcu_exp_runtime_mode() |
|
* core_initcall() is invoked, at which point everything is expedited.) |
|
*/ |
|
bool rcu_gp_is_normal(void) |
|
{ |
|
return READ_ONCE(rcu_normal) && |
|
rcu_scheduler_active != RCU_SCHEDULER_INIT; |
|
} |
|
EXPORT_SYMBOL_GPL(rcu_gp_is_normal); |
|
|
|
static atomic_t rcu_expedited_nesting = |
|
ATOMIC_INIT(IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT) ? 1 : 0); |
|
|
|
/* |
|
* Should normal grace-period primitives be expedited? Intended for |
|
* use within RCU. Note that this function takes the rcu_expedited |
|
* sysfs/boot variable and rcu_scheduler_active into account as well |
|
* as the rcu_expedite_gp() nesting. So looping on rcu_unexpedite_gp() |
|
* until rcu_gp_is_expedited() returns false is a -really- bad idea. |
|
*/ |
|
bool rcu_gp_is_expedited(void) |
|
{ |
|
return rcu_expedited || atomic_read(&rcu_expedited_nesting) || |
|
rcu_scheduler_active == RCU_SCHEDULER_INIT; |
|
} |
|
EXPORT_SYMBOL_GPL(rcu_gp_is_expedited); |
|
|
|
/** |
|
* rcu_expedite_gp - Expedite future RCU grace periods |
|
* |
|
* After a call to this function, future calls to synchronize_rcu() and |
|
* friends act as the corresponding synchronize_rcu_expedited() function |
|
* had instead been called. |
|
*/ |
|
void rcu_expedite_gp(void) |
|
{ |
|
atomic_inc(&rcu_expedited_nesting); |
|
} |
|
EXPORT_SYMBOL_GPL(rcu_expedite_gp); |
|
|
|
/** |
|
* rcu_unexpedite_gp - Cancel prior rcu_expedite_gp() invocation |
|
* |
|
* Undo a prior call to rcu_expedite_gp(). If all prior calls to |
|
* rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(), |
|
* and if the rcu_expedited sysfs/boot parameter is not set, then all |
|
* subsequent calls to synchronize_rcu() and friends will return to |
|
* their normal non-expedited behavior. |
|
*/ |
|
void rcu_unexpedite_gp(void) |
|
{ |
|
atomic_dec(&rcu_expedited_nesting); |
|
} |
|
EXPORT_SYMBOL_GPL(rcu_unexpedite_gp); |
|
|
|
/* |
|
* Inform RCU of the end of the in-kernel boot sequence. |
|
*/ |
|
void rcu_end_inkernel_boot(void) |
|
{ |
|
if (IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT)) |
|
rcu_unexpedite_gp(); |
|
if (rcu_normal_after_boot) |
|
WRITE_ONCE(rcu_normal, 1); |
|
} |
|
|
|
#endif /* #ifndef CONFIG_TINY_RCU */ |
|
|
|
#ifdef CONFIG_PREEMPT_RCU |
|
|
|
/* |
|
* Preemptible RCU implementation for rcu_read_lock(). |
|
* Just increment ->rcu_read_lock_nesting, shared state will be updated |
|
* if we block. |
|
*/ |
|
void __rcu_read_lock(void) |
|
{ |
|
current->rcu_read_lock_nesting++; |
|
barrier(); /* critical section after entry code. */ |
|
} |
|
EXPORT_SYMBOL_GPL(__rcu_read_lock); |
|
|
|
/* |
|
* Preemptible RCU implementation for rcu_read_unlock(). |
|
* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost |
|
* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then |
|
* invoke rcu_read_unlock_special() to clean up after a context switch |
|
* in an RCU read-side critical section and other special cases. |
|
*/ |
|
void __rcu_read_unlock(void) |
|
{ |
|
struct task_struct *t = current; |
|
|
|
if (t->rcu_read_lock_nesting != 1) { |
|
--t->rcu_read_lock_nesting; |
|
} else { |
|
barrier(); /* critical section before exit code. */ |
|
t->rcu_read_lock_nesting = INT_MIN; |
|
barrier(); /* assign before ->rcu_read_unlock_special load */ |
|
if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s))) |
|
rcu_read_unlock_special(t); |
|
barrier(); /* ->rcu_read_unlock_special load before assign */ |
|
t->rcu_read_lock_nesting = 0; |
|
} |
|
#ifdef CONFIG_PROVE_LOCKING |
|
{ |
|
int rrln = READ_ONCE(t->rcu_read_lock_nesting); |
|
|
|
WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); |
|
} |
|
#endif /* #ifdef CONFIG_PROVE_LOCKING */ |
|
} |
|
EXPORT_SYMBOL_GPL(__rcu_read_unlock); |
|
|
|
#endif /* #ifdef CONFIG_PREEMPT_RCU */ |
|
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC |
|
static struct lock_class_key rcu_lock_key; |
|
struct lockdep_map rcu_lock_map = |
|
STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); |
|
EXPORT_SYMBOL_GPL(rcu_lock_map); |
|
|
|
static struct lock_class_key rcu_bh_lock_key; |
|
struct lockdep_map rcu_bh_lock_map = |
|
STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key); |
|
EXPORT_SYMBOL_GPL(rcu_bh_lock_map); |
|
|
|
static struct lock_class_key rcu_sched_lock_key; |
|
struct lockdep_map rcu_sched_lock_map = |
|
STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key); |
|
EXPORT_SYMBOL_GPL(rcu_sched_lock_map); |
|
|
|
static struct lock_class_key rcu_callback_key; |
|
struct lockdep_map rcu_callback_map = |
|
STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key); |
|
EXPORT_SYMBOL_GPL(rcu_callback_map); |
|
|
|
int notrace debug_lockdep_rcu_enabled(void) |
|
{ |
|
return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && debug_locks && |
|
current->lockdep_recursion == 0; |
|
} |
|
EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); |
|
|
|
/** |
|
* rcu_read_lock_held() - might we be in RCU read-side critical section? |
|
* |
|
* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU |
|
* read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, |
|
* this assumes we are in an RCU read-side critical section unless it can |
|
* prove otherwise. This is useful for debug checks in functions that |
|
* require that they be called within an RCU read-side critical section. |
|
* |
|
* Checks debug_lockdep_rcu_enabled() to prevent false positives during boot |
|
* and while lockdep is disabled. |
|
* |
|
* Note that rcu_read_lock() and the matching rcu_read_unlock() must |
|
* occur in the same context, for example, it is illegal to invoke |
|
* rcu_read_unlock() in process context if the matching rcu_read_lock() |
|
* was invoked from within an irq handler. |
|
* |
|
* Note that rcu_read_lock() is disallowed if the CPU is either idle or |
|
* offline from an RCU perspective, so check for those as well. |
|
*/ |
|
int rcu_read_lock_held(void) |
|
{ |
|
if (!debug_lockdep_rcu_enabled()) |
|
return 1; |
|
if (!rcu_is_watching()) |
|
return 0; |
|
if (!rcu_lockdep_current_cpu_online()) |
|
return 0; |
|
return lock_is_held(&rcu_lock_map); |
|
} |
|
EXPORT_SYMBOL_GPL(rcu_read_lock_held); |
|
|
|
/** |
|
* rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? |
|
* |
|
* Check for bottom half being disabled, which covers both the |
|
* CONFIG_PROVE_RCU and not cases. Note that if someone uses |
|
* rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) |
|
* will show the situation. This is useful for debug checks in functions |
|
* that require that they be called within an RCU read-side critical |
|
* section. |
|
* |
|
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot. |
|
* |
|
* Note that rcu_read_lock() is disallowed if the CPU is either idle or |
|
* offline from an RCU perspective, so check for those as well. |
|
*/ |
|
int rcu_read_lock_bh_held(void) |
|
{ |
|
if (!debug_lockdep_rcu_enabled()) |
|
return 1; |
|
if (!rcu_is_watching()) |
|
return 0; |
|
if (!rcu_lockdep_current_cpu_online()) |
|
return 0; |
|
return in_softirq() || irqs_disabled(); |
|
} |
|
EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); |
|
|
|
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
|
|
|
/** |
|
* wakeme_after_rcu() - Callback function to awaken a task after grace period |
|
* @head: Pointer to rcu_head member within rcu_synchronize structure |
|
* |
|
* Awaken the corresponding task now that a grace period has elapsed. |
|
*/ |
|
void wakeme_after_rcu(struct rcu_head *head) |
|
{ |
|
struct rcu_synchronize *rcu; |
|
|
|
rcu = container_of(head, struct rcu_synchronize, head); |
|
complete(&rcu->completion); |
|
} |
|
EXPORT_SYMBOL_GPL(wakeme_after_rcu); |
|
|
|
void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array, |
|
struct rcu_synchronize *rs_array) |
|
{ |
|
int i; |
|
|
|
/* Initialize and register callbacks for each flavor specified. */ |
|
for (i = 0; i < n; i++) { |
|
if (checktiny && |
|
(crcu_array[i] == call_rcu || |
|
crcu_array[i] == call_rcu_bh)) { |
|
might_sleep(); |
|
continue; |
|
} |
|
init_rcu_head_on_stack(&rs_array[i].head); |
|
init_completion(&rs_array[i].completion); |
|
(crcu_array[i])(&rs_array[i].head, wakeme_after_rcu); |
|
} |
|
|
|
/* Wait for all callbacks to be invoked. */ |
|
for (i = 0; i < n; i++) { |
|
if (checktiny && |
|
(crcu_array[i] == call_rcu || |
|
crcu_array[i] == call_rcu_bh)) |
|
continue; |
|
wait_for_completion(&rs_array[i].completion); |
|
destroy_rcu_head_on_stack(&rs_array[i].head); |
|
} |
|
} |
|
EXPORT_SYMBOL_GPL(__wait_rcu_gp); |
|
|
|
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD |
|
void init_rcu_head(struct rcu_head *head) |
|
{ |
|
debug_object_init(head, &rcuhead_debug_descr); |
|
} |
|
|
|
void destroy_rcu_head(struct rcu_head *head) |
|
{ |
|
debug_object_free(head, &rcuhead_debug_descr); |
|
} |
|
|
|
static bool rcuhead_is_static_object(void *addr) |
|
{ |
|
return true; |
|
} |
|
|
|
/** |
|
* init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects |
|
* @head: pointer to rcu_head structure to be initialized |
|
* |
|
* This function informs debugobjects of a new rcu_head structure that |
|
* has been allocated as an auto variable on the stack. This function |
|
* is not required for rcu_head structures that are statically defined or |
|
* that are dynamically allocated on the heap. This function has no |
|
* effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. |
|
*/ |
|
void init_rcu_head_on_stack(struct rcu_head *head) |
|
{ |
|
debug_object_init_on_stack(head, &rcuhead_debug_descr); |
|
} |
|
EXPORT_SYMBOL_GPL(init_rcu_head_on_stack); |
|
|
|
/** |
|
* destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects |
|
* @head: pointer to rcu_head structure to be initialized |
|
* |
|
* This function informs debugobjects that an on-stack rcu_head structure |
|
* is about to go out of scope. As with init_rcu_head_on_stack(), this |
|
* function is not required for rcu_head structures that are statically |
|
* defined or that are dynamically allocated on the heap. Also as with |
|
* init_rcu_head_on_stack(), this function has no effect for |
|
* !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. |
|
*/ |
|
void destroy_rcu_head_on_stack(struct rcu_head *head) |
|
{ |
|
debug_object_free(head, &rcuhead_debug_descr); |
|
} |
|
EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack); |
|
|
|
struct debug_obj_descr rcuhead_debug_descr = { |
|
.name = "rcu_head", |
|
.is_static_object = rcuhead_is_static_object, |
|
}; |
|
EXPORT_SYMBOL_GPL(rcuhead_debug_descr); |
|
#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
|
|
|
#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE) |
|
void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp, |
|
unsigned long secs, |
|
unsigned long c_old, unsigned long c) |
|
{ |
|
trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c); |
|
} |
|
EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); |
|
#else |
|
#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ |
|
do { } while (0) |
|
#endif |
|
|
|
#ifdef CONFIG_RCU_STALL_COMMON |
|
|
|
#ifdef CONFIG_PROVE_RCU |
|
#define RCU_STALL_DELAY_DELTA (5 * HZ) |
|
#else |
|
#define RCU_STALL_DELAY_DELTA 0 |
|
#endif |
|
|
|
int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */ |
|
static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; |
|
|
|
module_param(rcu_cpu_stall_suppress, int, 0644); |
|
module_param(rcu_cpu_stall_timeout, int, 0644); |
|
|
|
int rcu_jiffies_till_stall_check(void) |
|
{ |
|
int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout); |
|
|
|
/* |
|
* Limit check must be consistent with the Kconfig limits |
|
* for CONFIG_RCU_CPU_STALL_TIMEOUT. |
|
*/ |
|
if (till_stall_check < 3) { |
|
WRITE_ONCE(rcu_cpu_stall_timeout, 3); |
|
till_stall_check = 3; |
|
} else if (till_stall_check > 300) { |
|
WRITE_ONCE(rcu_cpu_stall_timeout, 300); |
|
till_stall_check = 300; |
|
} |
|
return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; |
|
} |
|
|
|
void rcu_sysrq_start(void) |
|
{ |
|
if (!rcu_cpu_stall_suppress) |
|
rcu_cpu_stall_suppress = 2; |
|
} |
|
|
|
void rcu_sysrq_end(void) |
|
{ |
|
if (rcu_cpu_stall_suppress == 2) |
|
rcu_cpu_stall_suppress = 0; |
|
} |
|
|
|
static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) |
|
{ |
|
rcu_cpu_stall_suppress = 1; |
|
return NOTIFY_DONE; |
|
} |
|
|
|
static struct notifier_block rcu_panic_block = { |
|
.notifier_call = rcu_panic, |
|
}; |
|
|
|
static int __init check_cpu_stall_init(void) |
|
{ |
|
atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block); |
|
return 0; |
|
} |
|
early_initcall(check_cpu_stall_init); |
|
|
|
#endif /* #ifdef CONFIG_RCU_STALL_COMMON */ |
|
|
|
#ifdef CONFIG_TASKS_RCU |
|
|
|
/* |
|
* Simple variant of RCU whose quiescent states are voluntary context switch, |
|
* user-space execution, and idle. As such, grace periods can take one good |
|
* long time. There are no read-side primitives similar to rcu_read_lock() |
|
* and rcu_read_unlock() because this implementation is intended to get |
|
* the system into a safe state for some of the manipulations involved in |
|
* tracing and the like. Finally, this implementation does not support |
|
* high call_rcu_tasks() rates from multiple CPUs. If this is required, |
|
* per-CPU callback lists will be needed. |
|
*/ |
|
|
|
/* Global list of callbacks and associated lock. */ |
|
static struct rcu_head *rcu_tasks_cbs_head; |
|
static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head; |
|
static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq); |
|
static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock); |
|
|
|
/* Track exiting tasks in order to allow them to be waited for. */ |
|
DEFINE_SRCU(tasks_rcu_exit_srcu); |
|
|
|
/* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */ |
|
static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10; |
|
module_param(rcu_task_stall_timeout, int, 0644); |
|
|
|
static void rcu_spawn_tasks_kthread(void); |
|
static struct task_struct *rcu_tasks_kthread_ptr; |
|
|
|
/* |
|
* Post an RCU-tasks callback. First call must be from process context |
|
* after the scheduler if fully operational. |
|
*/ |
|
void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) |
|
{ |
|
unsigned long flags; |
|
bool needwake; |
|
bool havetask = READ_ONCE(rcu_tasks_kthread_ptr); |
|
|
|
rhp->next = NULL; |
|
rhp->func = func; |
|
raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags); |
|
needwake = !rcu_tasks_cbs_head; |
|
*rcu_tasks_cbs_tail = rhp; |
|
rcu_tasks_cbs_tail = &rhp->next; |
|
raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); |
|
/* We can't create the thread unless interrupts are enabled. */ |
|
if ((needwake && havetask) || |
|
(!havetask && !irqs_disabled_flags(flags))) { |
|
rcu_spawn_tasks_kthread(); |
|
wake_up(&rcu_tasks_cbs_wq); |
|
} |
|
} |
|
EXPORT_SYMBOL_GPL(call_rcu_tasks); |
|
|
|
/** |
|
* synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed. |
|
* |
|
* Control will return to the caller some time after a full rcu-tasks |
|
* grace period has elapsed, in other words after all currently |
|
* executing rcu-tasks read-side critical sections have elapsed. These |
|
* read-side critical sections are delimited by calls to schedule(), |
|
* cond_resched_rcu_qs(), idle execution, userspace execution, calls |
|
* to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched(). |
|
* |
|
* This is a very specialized primitive, intended only for a few uses in |
|
* tracing and other situations requiring manipulation of function |
|
* preambles and profiling hooks. The synchronize_rcu_tasks() function |
|
* is not (yet) intended for heavy use from multiple CPUs. |
|
* |
|
* Note that this guarantee implies further memory-ordering guarantees. |
|
* On systems with more than one CPU, when synchronize_rcu_tasks() returns, |
|
* each CPU is guaranteed to have executed a full memory barrier since the |
|
* end of its last RCU-tasks read-side critical section whose beginning |
|
* preceded the call to synchronize_rcu_tasks(). In addition, each CPU |
|
* having an RCU-tasks read-side critical section that extends beyond |
|
* the return from synchronize_rcu_tasks() is guaranteed to have executed |
|
* a full memory barrier after the beginning of synchronize_rcu_tasks() |
|
* and before the beginning of that RCU-tasks read-side critical section. |
|
* Note that these guarantees include CPUs that are offline, idle, or |
|
* executing in user mode, as well as CPUs that are executing in the kernel. |
|
* |
|
* Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned |
|
* to its caller on CPU B, then both CPU A and CPU B are guaranteed |
|
* to have executed a full memory barrier during the execution of |
|
* synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU |
|
* (but again only if the system has more than one CPU). |
|
*/ |
|
void synchronize_rcu_tasks(void) |
|
{ |
|
/* Complain if the scheduler has not started. */ |
|
RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE, |
|
"synchronize_rcu_tasks called too soon"); |
|
|
|
/* Wait for the grace period. */ |
|
wait_rcu_gp(call_rcu_tasks); |
|
} |
|
EXPORT_SYMBOL_GPL(synchronize_rcu_tasks); |
|
|
|
/** |
|
* rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks. |
|
* |
|
* Although the current implementation is guaranteed to wait, it is not |
|
* obligated to, for example, if there are no pending callbacks. |
|
*/ |
|
void rcu_barrier_tasks(void) |
|
{ |
|
/* There is only one callback queue, so this is easy. ;-) */ |
|
synchronize_rcu_tasks(); |
|
} |
|
EXPORT_SYMBOL_GPL(rcu_barrier_tasks); |
|
|
|
/* See if tasks are still holding out, complain if so. */ |
|
static void check_holdout_task(struct task_struct *t, |
|
bool needreport, bool *firstreport) |
|
{ |
|
int cpu; |
|
|
|
if (!READ_ONCE(t->rcu_tasks_holdout) || |
|
t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) || |
|
!READ_ONCE(t->on_rq) || |
|
(IS_ENABLED(CONFIG_NO_HZ_FULL) && |
|
!is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) { |
|
WRITE_ONCE(t->rcu_tasks_holdout, false); |
|
list_del_init(&t->rcu_tasks_holdout_list); |
|
put_task_struct(t); |
|
return; |
|
} |
|
if (!needreport) |
|
return; |
|
if (*firstreport) { |
|
pr_err("INFO: rcu_tasks detected stalls on tasks:\n"); |
|
*firstreport = false; |
|
} |
|
cpu = task_cpu(t); |
|
pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n", |
|
t, ".I"[is_idle_task(t)], |
|
"N."[cpu < 0 || !tick_nohz_full_cpu(cpu)], |
|
t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout, |
|
t->rcu_tasks_idle_cpu, cpu); |
|
sched_show_task(t); |
|
} |
|
|
|
/* RCU-tasks kthread that detects grace periods and invokes callbacks. */ |
|
static int __noreturn rcu_tasks_kthread(void *arg) |
|
{ |
|
unsigned long flags; |
|
struct task_struct *g, *t; |
|
unsigned long lastreport; |
|
struct rcu_head *list; |
|
struct rcu_head *next; |
|
LIST_HEAD(rcu_tasks_holdouts); |
|
|
|
/* Run on housekeeping CPUs by default. Sysadm can move if desired. */ |
|
housekeeping_affine(current); |
|
|
|
/* |
|
* Each pass through the following loop makes one check for |
|
* newly arrived callbacks, and, if there are some, waits for |
|
* one RCU-tasks grace period and then invokes the callbacks. |
|
* This loop is terminated by the system going down. ;-) |
|
*/ |
|
for (;;) { |
|
|
|
/* Pick up any new callbacks. */ |
|
raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags); |
|
list = rcu_tasks_cbs_head; |
|
rcu_tasks_cbs_head = NULL; |
|
rcu_tasks_cbs_tail = &rcu_tasks_cbs_head; |
|
raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); |
|
|
|
/* If there were none, wait a bit and start over. */ |
|
if (!list) { |
|
wait_event_interruptible(rcu_tasks_cbs_wq, |
|
rcu_tasks_cbs_head); |
|
if (!rcu_tasks_cbs_head) { |
|
WARN_ON(signal_pending(current)); |
|
schedule_timeout_interruptible(HZ/10); |
|
} |
|
continue; |
|
} |
|
|
|
/* |
|
* Wait for all pre-existing t->on_rq and t->nvcsw |
|
* transitions to complete. Invoking synchronize_sched() |
|
* suffices because all these transitions occur with |
|
* interrupts disabled. Without this synchronize_sched(), |
|
* a read-side critical section that started before the |
|
* grace period might be incorrectly seen as having started |
|
* after the grace period. |
|
* |
|
* This synchronize_sched() also dispenses with the |
|
* need for a memory barrier on the first store to |
|
* ->rcu_tasks_holdout, as it forces the store to happen |
|
* after the beginning of the grace period. |
|
*/ |
|
synchronize_sched(); |
|
|
|
/* |
|
* There were callbacks, so we need to wait for an |
|
* RCU-tasks grace period. Start off by scanning |
|
* the task list for tasks that are not already |
|
* voluntarily blocked. Mark these tasks and make |
|
* a list of them in rcu_tasks_holdouts. |
|
*/ |
|
rcu_read_lock(); |
|
for_each_process_thread(g, t) { |
|
if (t != current && READ_ONCE(t->on_rq) && |
|
!is_idle_task(t)) { |
|
get_task_struct(t); |
|
t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw); |
|
WRITE_ONCE(t->rcu_tasks_holdout, true); |
|
list_add(&t->rcu_tasks_holdout_list, |
|
&rcu_tasks_holdouts); |
|
} |
|
} |
|
rcu_read_unlock(); |
|
|
|
/* |
|
* Wait for tasks that are in the process of exiting. |
|
* This does only part of the job, ensuring that all |
|
* tasks that were previously exiting reach the point |
|
* where they have disabled preemption, allowing the |
|
* later synchronize_sched() to finish the job. |
|
*/ |
|
synchronize_srcu(&tasks_rcu_exit_srcu); |
|
|
|
/* |
|
* Each pass through the following loop scans the list |
|
* of holdout tasks, removing any that are no longer |
|
* holdouts. When the list is empty, we are done. |
|
*/ |
|
lastreport = jiffies; |
|
while (!list_empty(&rcu_tasks_holdouts)) { |
|
bool firstreport; |
|
bool needreport; |
|
int rtst; |
|
struct task_struct *t1; |
|
|
|
schedule_timeout_interruptible(HZ); |
|
rtst = READ_ONCE(rcu_task_stall_timeout); |
|
needreport = rtst > 0 && |
|
time_after(jiffies, lastreport + rtst); |
|
if (needreport) |
|
lastreport = jiffies; |
|
firstreport = true; |
|
WARN_ON(signal_pending(current)); |
|
list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts, |
|
rcu_tasks_holdout_list) { |
|
check_holdout_task(t, needreport, &firstreport); |
|
cond_resched(); |
|
} |
|
} |
|
|
|
/* |
|
* Because ->on_rq and ->nvcsw are not guaranteed |
|
* to have a full memory barriers prior to them in the |
|
* schedule() path, memory reordering on other CPUs could |
|
* cause their RCU-tasks read-side critical sections to |
|
* extend past the end of the grace period. However, |
|
* because these ->nvcsw updates are carried out with |
|
* interrupts disabled, we can use synchronize_sched() |
|
* to force the needed ordering on all such CPUs. |
|
* |
|
* This synchronize_sched() also confines all |
|
* ->rcu_tasks_holdout accesses to be within the grace |
|
* period, avoiding the need for memory barriers for |
|
* ->rcu_tasks_holdout accesses. |
|
* |
|
* In addition, this synchronize_sched() waits for exiting |
|
* tasks to complete their final preempt_disable() region |
|
* of execution, cleaning up after the synchronize_srcu() |
|
* above. |
|
*/ |
|
synchronize_sched(); |
|
|
|
/* Invoke the callbacks. */ |
|
while (list) { |
|
next = list->next; |
|
local_bh_disable(); |
|
list->func(list); |
|
local_bh_enable(); |
|
list = next; |
|
cond_resched(); |
|
} |
|
schedule_timeout_uninterruptible(HZ/10); |
|
} |
|
} |
|
|
|
/* Spawn rcu_tasks_kthread() at first call to call_rcu_tasks(). */ |
|
static void rcu_spawn_tasks_kthread(void) |
|
{ |
|
static DEFINE_MUTEX(rcu_tasks_kthread_mutex); |
|
struct task_struct *t; |
|
|
|
if (READ_ONCE(rcu_tasks_kthread_ptr)) { |
|
smp_mb(); /* Ensure caller sees full kthread. */ |
|
return; |
|
} |
|
mutex_lock(&rcu_tasks_kthread_mutex); |
|
if (rcu_tasks_kthread_ptr) { |
|
mutex_unlock(&rcu_tasks_kthread_mutex); |
|
return; |
|
} |
|
t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread"); |
|
BUG_ON(IS_ERR(t)); |
|
smp_mb(); /* Ensure others see full kthread. */ |
|
WRITE_ONCE(rcu_tasks_kthread_ptr, t); |
|
mutex_unlock(&rcu_tasks_kthread_mutex); |
|
} |
|
|
|
#endif /* #ifdef CONFIG_TASKS_RCU */ |
|
|
|
/* |
|
* Test each non-SRCU synchronous grace-period wait API. This is |
|
* useful just after a change in mode for these primitives, and |
|
* during early boot. |
|
*/ |
|
void rcu_test_sync_prims(void) |
|
{ |
|
if (!IS_ENABLED(CONFIG_PROVE_RCU)) |
|
return; |
|
synchronize_rcu(); |
|
synchronize_rcu_bh(); |
|
synchronize_sched(); |
|
synchronize_rcu_expedited(); |
|
synchronize_rcu_bh_expedited(); |
|
synchronize_sched_expedited(); |
|
} |
|
|
|
#ifdef CONFIG_PROVE_RCU |
|
|
|
/* |
|
* Early boot self test parameters, one for each flavor |
|
*/ |
|
static bool rcu_self_test; |
|
static bool rcu_self_test_bh; |
|
static bool rcu_self_test_sched; |
|
|
|
module_param(rcu_self_test, bool, 0444); |
|
module_param(rcu_self_test_bh, bool, 0444); |
|
module_param(rcu_self_test_sched, bool, 0444); |
|
|
|
static int rcu_self_test_counter; |
|
|
|
static void test_callback(struct rcu_head *r) |
|
{ |
|
rcu_self_test_counter++; |
|
pr_info("RCU test callback executed %d\n", rcu_self_test_counter); |
|
} |
|
|
|
static void early_boot_test_call_rcu(void) |
|
{ |
|
static struct rcu_head head; |
|
|
|
call_rcu(&head, test_callback); |
|
} |
|
|
|
static void early_boot_test_call_rcu_bh(void) |
|
{ |
|
static struct rcu_head head; |
|
|
|
call_rcu_bh(&head, test_callback); |
|
} |
|
|
|
static void early_boot_test_call_rcu_sched(void) |
|
{ |
|
static struct rcu_head head; |
|
|
|
call_rcu_sched(&head, test_callback); |
|
} |
|
|
|
void rcu_early_boot_tests(void) |
|
{ |
|
pr_info("Running RCU self tests\n"); |
|
|
|
if (rcu_self_test) |
|
early_boot_test_call_rcu(); |
|
if (rcu_self_test_bh) |
|
early_boot_test_call_rcu_bh(); |
|
if (rcu_self_test_sched) |
|
early_boot_test_call_rcu_sched(); |
|
rcu_test_sync_prims(); |
|
} |
|
|
|
static int rcu_verify_early_boot_tests(void) |
|
{ |
|
int ret = 0; |
|
int early_boot_test_counter = 0; |
|
|
|
if (rcu_self_test) { |
|
early_boot_test_counter++; |
|
rcu_barrier(); |
|
} |
|
if (rcu_self_test_bh) { |
|
early_boot_test_counter++; |
|
rcu_barrier_bh(); |
|
} |
|
if (rcu_self_test_sched) { |
|
early_boot_test_counter++; |
|
rcu_barrier_sched(); |
|
} |
|
|
|
if (rcu_self_test_counter != early_boot_test_counter) { |
|
WARN_ON(1); |
|
ret = -1; |
|
} |
|
|
|
return ret; |
|
} |
|
late_initcall(rcu_verify_early_boot_tests); |
|
#else |
|
void rcu_early_boot_tests(void) {} |
|
#endif /* CONFIG_PROVE_RCU */
|
|
|