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204 lines
6.3 KiB
204 lines
6.3 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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/* rwsem.h: R/W semaphores, public interface |
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* |
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* Written by David Howells ([email protected]). |
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* Derived from asm-i386/semaphore.h |
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*/ |
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#ifndef _LINUX_RWSEM_H |
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#define _LINUX_RWSEM_H |
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#include <linux/linkage.h> |
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#include <linux/types.h> |
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#include <linux/kernel.h> |
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#include <linux/list.h> |
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#include <linux/spinlock.h> |
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#include <linux/atomic.h> |
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#include <linux/err.h> |
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#ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
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#include <linux/osq_lock.h> |
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#endif |
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/* |
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* For an uncontended rwsem, count and owner are the only fields a task |
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* needs to touch when acquiring the rwsem. So they are put next to each |
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* other to increase the chance that they will share the same cacheline. |
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* |
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* In a contended rwsem, the owner is likely the most frequently accessed |
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* field in the structure as the optimistic waiter that holds the osq lock |
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* will spin on owner. For an embedded rwsem, other hot fields in the |
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* containing structure should be moved further away from the rwsem to |
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* reduce the chance that they will share the same cacheline causing |
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* cacheline bouncing problem. |
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*/ |
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struct rw_semaphore { |
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atomic_long_t count; |
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/* |
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* Write owner or one of the read owners as well flags regarding |
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* the current state of the rwsem. Can be used as a speculative |
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* check to see if the write owner is running on the cpu. |
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*/ |
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atomic_long_t owner; |
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#ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
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struct optimistic_spin_queue osq; /* spinner MCS lock */ |
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#endif |
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raw_spinlock_t wait_lock; |
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struct list_head wait_list; |
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#ifdef CONFIG_DEBUG_RWSEMS |
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void *magic; |
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#endif |
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#ifdef CONFIG_DEBUG_LOCK_ALLOC |
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struct lockdep_map dep_map; |
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#endif |
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}; |
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/* In all implementations count != 0 means locked */ |
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static inline int rwsem_is_locked(struct rw_semaphore *sem) |
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{ |
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return atomic_long_read(&sem->count) != 0; |
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} |
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#define RWSEM_UNLOCKED_VALUE 0L |
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#define __RWSEM_COUNT_INIT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) |
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/* Common initializer macros and functions */ |
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#ifdef CONFIG_DEBUG_LOCK_ALLOC |
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# define __RWSEM_DEP_MAP_INIT(lockname) \ |
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.dep_map = { \ |
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.name = #lockname, \ |
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.wait_type_inner = LD_WAIT_SLEEP, \ |
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}, |
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#else |
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# define __RWSEM_DEP_MAP_INIT(lockname) |
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#endif |
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#ifdef CONFIG_DEBUG_RWSEMS |
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# define __RWSEM_DEBUG_INIT(lockname) .magic = &lockname, |
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#else |
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# define __RWSEM_DEBUG_INIT(lockname) |
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#endif |
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#ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
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#define __RWSEM_OPT_INIT(lockname) .osq = OSQ_LOCK_UNLOCKED, |
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#else |
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#define __RWSEM_OPT_INIT(lockname) |
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#endif |
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#define __RWSEM_INITIALIZER(name) \ |
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{ __RWSEM_COUNT_INIT(name), \ |
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.owner = ATOMIC_LONG_INIT(0), \ |
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__RWSEM_OPT_INIT(name) \ |
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.wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),\ |
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.wait_list = LIST_HEAD_INIT((name).wait_list), \ |
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__RWSEM_DEBUG_INIT(name) \ |
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__RWSEM_DEP_MAP_INIT(name) } |
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#define DECLARE_RWSEM(name) \ |
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struct rw_semaphore name = __RWSEM_INITIALIZER(name) |
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extern void __init_rwsem(struct rw_semaphore *sem, const char *name, |
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struct lock_class_key *key); |
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#define init_rwsem(sem) \ |
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do { \ |
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static struct lock_class_key __key; \ |
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\ |
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__init_rwsem((sem), #sem, &__key); \ |
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} while (0) |
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/* |
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* This is the same regardless of which rwsem implementation that is being used. |
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* It is just a heuristic meant to be called by somebody alreadying holding the |
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* rwsem to see if somebody from an incompatible type is wanting access to the |
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* lock. |
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*/ |
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static inline int rwsem_is_contended(struct rw_semaphore *sem) |
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{ |
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return !list_empty(&sem->wait_list); |
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} |
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/* |
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* lock for reading |
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*/ |
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extern void down_read(struct rw_semaphore *sem); |
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extern int __must_check down_read_interruptible(struct rw_semaphore *sem); |
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extern int __must_check down_read_killable(struct rw_semaphore *sem); |
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/* |
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* trylock for reading -- returns 1 if successful, 0 if contention |
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*/ |
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extern int down_read_trylock(struct rw_semaphore *sem); |
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/* |
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* lock for writing |
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*/ |
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extern void down_write(struct rw_semaphore *sem); |
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extern int __must_check down_write_killable(struct rw_semaphore *sem); |
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/* |
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* trylock for writing -- returns 1 if successful, 0 if contention |
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*/ |
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extern int down_write_trylock(struct rw_semaphore *sem); |
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/* |
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* release a read lock |
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*/ |
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extern void up_read(struct rw_semaphore *sem); |
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/* |
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* release a write lock |
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*/ |
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extern void up_write(struct rw_semaphore *sem); |
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/* |
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* downgrade write lock to read lock |
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*/ |
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extern void downgrade_write(struct rw_semaphore *sem); |
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#ifdef CONFIG_DEBUG_LOCK_ALLOC |
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/* |
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* nested locking. NOTE: rwsems are not allowed to recurse |
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* (which occurs if the same task tries to acquire the same |
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* lock instance multiple times), but multiple locks of the |
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* same lock class might be taken, if the order of the locks |
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* is always the same. This ordering rule can be expressed |
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* to lockdep via the _nested() APIs, but enumerating the |
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* subclasses that are used. (If the nesting relationship is |
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* static then another method for expressing nested locking is |
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* the explicit definition of lock class keys and the use of |
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* lockdep_set_class() at lock initialization time. |
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* See Documentation/locking/lockdep-design.rst for more details.) |
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*/ |
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extern void down_read_nested(struct rw_semaphore *sem, int subclass); |
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extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass); |
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extern void down_write_nested(struct rw_semaphore *sem, int subclass); |
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extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass); |
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extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); |
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# define down_write_nest_lock(sem, nest_lock) \ |
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do { \ |
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typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ |
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_down_write_nest_lock(sem, &(nest_lock)->dep_map); \ |
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} while (0); |
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/* |
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* Take/release a lock when not the owner will release it. |
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* |
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* [ This API should be avoided as much as possible - the |
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* proper abstraction for this case is completions. ] |
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*/ |
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extern void down_read_non_owner(struct rw_semaphore *sem); |
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extern void up_read_non_owner(struct rw_semaphore *sem); |
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#else |
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# define down_read_nested(sem, subclass) down_read(sem) |
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# define down_read_killable_nested(sem, subclass) down_read_killable(sem) |
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# define down_write_nest_lock(sem, nest_lock) down_write(sem) |
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# define down_write_nested(sem, subclass) down_write(sem) |
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# define down_write_killable_nested(sem, subclass) down_write_killable(sem) |
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# define down_read_non_owner(sem) down_read(sem) |
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# define up_read_non_owner(sem) up_read(sem) |
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#endif |
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#endif /* _LINUX_RWSEM_H */
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