![Davidlohr Bueso](/assets/img/avatar_default.png)
Optimistic spinning is only used by the xadd variant of rw-semaphores. Make sure that we use the old version of the __RWSEM_INITIALIZER macro for systems that rely on the spinlock one, otherwise warnings can be triggered, such as the following reported on an arm box: ipc/ipcns_notifier.c:22:8: warning: excess elements in struct initializer [enabled by default] ipc/ipcns_notifier.c:22:8: warning: (near initialization for 'ipcns_chain.rwsem') [enabled by default] ipc/ipcns_notifier.c:22:8: warning: excess elements in struct initializer [enabled by default] ipc/ipcns_notifier.c:22:8: warning: (near initialization for 'ipcns_chain.rwsem') [enabled by default] Signed-off-by: Davidlohr Bueso <davidlohr@hp.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Cc: Michel Lespinasse <walken@google.com> Cc: Peter Hurley <peter@hurleysoftware.com> Cc: Alex Shi <alex.shi@linaro.org> Cc: Rik van Riel <riel@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Jason Low <jason.low2@hp.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Chris Mason <clm@fb.com> Cc: Josef Bacik <jbacik@fusionio.com> Link: http://lkml.kernel.org/r/1400545677.6399.10.camel@buesod1.americas.hpqcorp.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
183 lines
5.2 KiB
C
183 lines
5.2 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 optimistic_spin_queue;
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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_SMP
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/*
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* Write owner. Used as a speculative check to see
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* if the owner is running on the cpu.
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*/
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struct task_struct *owner;
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struct optimistic_spin_queue *osq; /* spinner MCS lock */
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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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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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#if defined(CONFIG_SMP) && !defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
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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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NULL, /* owner */ \
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NULL /* mcs lock */ \
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__RWSEM_DEP_MAP_INIT(name) }
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#else
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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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#endif
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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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/*
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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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