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84759c6d18
This reverts commit 11b80f459a.
Bcache needs rw semaphores for cache coherency in writeback mode -
writes have to take a read lock on a per cache device rw sem, and
release it when the bio completes.
But since this is for bios it's naturally not in the context of the
process that originally took the lock.
Signed-off-by: Kent Overstreet <koverstreet@google.com>
CC: Christoph Hellwig <hch@infradead.org>
CC: David Howells <dhowells@redhat.com>
152 lines
4.3 KiB
C
152 lines
4.3 KiB
C
/* rwsem.h: R/W semaphores, public interface
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*
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* Written by David Howells (dhowells@redhat.com).
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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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struct rw_semaphore;
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#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
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#include <linux/rwsem-spinlock.h> /* use a generic implementation */
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#else
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/* All arch specific implementations share the same struct */
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struct rw_semaphore {
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long count;
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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_LOCK_ALLOC
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struct lockdep_map dep_map;
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#endif
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};
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extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
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extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
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extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
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extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
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/* Include the arch specific part */
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#include <asm/rwsem.h>
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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 sem->count != 0;
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}
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#endif
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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) , .dep_map = { .name = #lockname }
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#else
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# define __RWSEM_DEP_MAP_INIT(lockname)
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#endif
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#define __RWSEM_INITIALIZER(name) \
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{ RWSEM_UNLOCKED_VALUE, \
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__RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \
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LIST_HEAD_INIT((name).wait_list) \
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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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* lock for reading
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*/
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extern void down_read(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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/*
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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/lockdep-design.txt 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 void down_write_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_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_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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