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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>
zero-colors
Kirill Tkhai 2017-06-19 21:02:12 +03:00 committed by Ingo Molnar
parent 50972fe78f
commit 0aa1125fa8
2 changed files with 29 additions and 9 deletions
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1
include/linux/rwsem-spinlock.h
View File

@ -32,6 +32,7 @@ struct rw_semaphore {
#define RWSEM_UNLOCKED_VALUE 0x00000000
extern void __down_read(struct rw_semaphore *sem);
extern int __must_check __down_read_killable(struct rw_semaphore *sem);
extern int __down_read_trylock(struct rw_semaphore *sem);
extern void __down_write(struct rw_semaphore *sem);
extern int __must_check __down_write_killable(struct rw_semaphore *sem);

37
kernel/locking/rwsem-spinlock.c
View File

@ -126,7 +126,7 @@ __rwsem_wake_one_writer(struct rw_semaphore *sem)
/*
* get a read lock on the semaphore
*/
void __sched __down_read(struct rw_semaphore *sem)
int __sched __down_read_common(struct rw_semaphore *sem, int state)
{
struct rwsem_waiter waiter;
unsigned long flags;
@ -140,8 +140,6 @@ void __sched __down_read(struct rw_semaphore *sem)
goto out;
}
set_current_state(TASK_UNINTERRUPTIBLE);
/* set up my own style of waitqueue */
waiter.task = current;
waiter.type = RWSEM_WAITING_FOR_READ;
@ -149,20 +147,41 @@ void __sched __down_read(struct rw_semaphore *sem)
list_add_tail(&waiter.list, &sem->wait_list);
/* we don't need to touch the semaphore struct anymore */
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
/* wait to be given the lock */
for (;;) {
if (!waiter.task)
break;
if (signal_pending_state(state, current))
goto out_nolock;
set_current_state(state);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
schedule();
set_current_state(TASK_UNINTERRUPTIBLE);
raw_spin_lock_irqsave(&sem->wait_lock, flags);
}
__set_current_state(TASK_RUNNING);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
out:
;
return 0;
out_nolock:
/*
* We didn't take the lock, so that there is a writer, which
* is owner or the first waiter of the sem. If it's a waiter,
* it will be woken by current owner. Not need to wake anybody.
*/
list_del(&waiter.list);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
return -EINTR;
}
void __sched __down_read(struct rw_semaphore *sem)
{
__down_read_common(sem, TASK_UNINTERRUPTIBLE);
}
int __sched __down_read_killable(struct rw_semaphore *sem)
{
return __down_read_common(sem, TASK_KILLABLE);
}
/*