2005-04-17 05:20:36 +07:00
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/* rwsem-spinlock.h: fallback C implementation
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*
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* Copyright (c) 2001 David Howells (dhowells@redhat.com).
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* - Derived partially from ideas by Andrea Arcangeli <andrea@suse.de>
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* - Derived also from comments by Linus
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*/
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#ifndef _LINUX_RWSEM_SPINLOCK_H
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#define _LINUX_RWSEM_SPINLOCK_H
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#ifndef _LINUX_RWSEM_H
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#error "please don't include linux/rwsem-spinlock.h directly, use linux/rwsem.h instead"
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#endif
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#ifdef __KERNEL__
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/*
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* the rw-semaphore definition
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2014-07-16 19:54:55 +07:00
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* - if count is 0 then there are no active readers or writers
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* - if count is +ve then that is the number of active readers
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* - if count is -1 then there is one active writer
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2005-04-17 05:20:36 +07:00
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* - if wait_list is not empty, then there are processes waiting for the semaphore
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*/
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struct rw_semaphore {
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2014-07-16 19:54:55 +07:00
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__s32 count;
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2010-02-24 15:54:54 +07:00
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raw_spinlock_t wait_lock;
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2005-04-17 05:20:36 +07:00
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struct list_head wait_list;
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2006-07-03 14:24:53 +07:00
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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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2005-04-17 05:20:36 +07:00
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};
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2011-01-27 03:06:00 +07:00
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#define RWSEM_UNLOCKED_VALUE 0x00000000
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2006-07-03 14:24:53 +07:00
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2008-02-14 06:03:15 +07:00
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extern void __down_read(struct rw_semaphore *sem);
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locking/rwsem-spinlock: Add killable versions of __down_read()
Rename __down_read() in __down_read_common() and teach it
to abort waiting in case of pending signals and killable
state argument passed.
Note, that we shouldn't wake anybody up in EINTR path, as:
We check for signal_pending_state() after (!waiter.task)
test and under spinlock. So, current task wasn't able to
be woken up. It may be in two cases: a writer is owner
of the sem, or a writer is a first waiter of the sem.
If a writer is owner of the sem, no one else may work
with it in parallel. It will wake somebody, when it
call up_write() or downgrade_write().
If a writer is the first waiter, it will be woken up,
when the last active reader releases the sem, and
sem->count became 0.
Also note, that set_current_state() may be moved down
to schedule() (after !waiter.task check), as all
assignments in this type of semaphore (including wake_up),
occur under spinlock, so we can't miss anything.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: arnd@arndb.de
Cc: avagin@virtuozzo.com
Cc: davem@davemloft.net
Cc: fenghua.yu@intel.com
Cc: gorcunov@virtuozzo.com
Cc: heiko.carstens@de.ibm.com
Cc: hpa@zytor.com
Cc: ink@jurassic.park.msu.ru
Cc: mattst88@gmail.com
Cc: rth@twiddle.net
Cc: schwidefsky@de.ibm.com
Cc: tony.luck@intel.com
Link: http://lkml.kernel.org/r/149789533283.9059.9829416940494747182.stgit@localhost.localdomain
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-20 01:02:12 +07:00
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extern int __must_check __down_read_killable(struct rw_semaphore *sem);
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2008-02-14 06:03:15 +07:00
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extern int __down_read_trylock(struct rw_semaphore *sem);
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extern void __down_write(struct rw_semaphore *sem);
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2016-04-07 22:12:26 +07:00
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extern int __must_check __down_write_killable(struct rw_semaphore *sem);
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2008-02-14 06:03:15 +07:00
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extern int __down_write_trylock(struct rw_semaphore *sem);
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extern void __up_read(struct rw_semaphore *sem);
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extern void __up_write(struct rw_semaphore *sem);
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extern void __downgrade_write(struct rw_semaphore *sem);
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2009-12-15 09:00:21 +07:00
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extern int rwsem_is_locked(struct rw_semaphore *sem);
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2005-10-30 08:15:44 +07:00
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2005-04-17 05:20:36 +07:00
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#endif /* __KERNEL__ */
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#endif /* _LINUX_RWSEM_SPINLOCK_H */
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