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Commit 72c1bbf3 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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futex: restartable futex_wait 



LTP test sigaction_16_24 fails, because it expects sem_wait to be restarted
if SA_RESTART is set.  sem_wait is implemented with futex_wait, that
currently doesn't support being restarted.  Ulrich confirms that the call
should be restartable.

Implement a restart_block method to handle the relative timeout, and allow
restarts.

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 9adef58b

kernel/futex.c

+51 −5
Original line number Diff line number Diff line
@@ -980,12 +980,15 @@ static void unqueue_me_pi(struct futex_q *q, struct futex_hash_bucket *hb) 
	drop_futex_key_refs(&q->key);

}



static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)

static long futex_wait_restart(struct restart_block *restart);

static int futex_wait_abstime(u32 __user *uaddr, u32 val,

			int timed, unsigned long abs_time)

{

	struct task_struct *curr = current;

	DECLARE_WAITQUEUE(wait, curr);

	struct futex_hash_bucket *hb;

	struct futex_q q;

	unsigned long time_left = 0;

	u32 uval;

	int ret;
@@ -1065,8 +1068,21 @@ static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time) 
	 * !list_empty() is safe here without any lock.

	 * q.lock_ptr != 0 is not safe, because of ordering against wakeup.

	 */

	if (likely(!list_empty(&q.list)))

		time = schedule_timeout(time);

	time_left = 0;

	if (likely(!list_empty(&q.list))) {

		unsigned long rel_time;



		if (timed) {

			unsigned long now = jiffies;

			if (time_after(now, abs_time))

				rel_time = 0;

			else

				rel_time = abs_time - now;

		} else

			rel_time = MAX_SCHEDULE_TIMEOUT;



		time_left = schedule_timeout(rel_time);

	}

	__set_current_state(TASK_RUNNING);



	/*
@@ -1077,13 +1093,25 @@ static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time) 
	/* If we were woken (and unqueued), we succeeded, whatever. */

	if (!unqueue_me(&q))

		return 0;

	if (time == 0)

	if (time_left == 0)

		return -ETIMEDOUT;



	/*

	 * We expect signal_pending(current), but another thread may

	 * have handled it for us already.

	 */

	return -EINTR;

	if (time_left == MAX_SCHEDULE_TIMEOUT)

		return -ERESTARTSYS;

	else {

		struct restart_block *restart;

		restart = &current_thread_info()->restart_block;

		restart->fn = futex_wait_restart;

		restart->arg0 = (unsigned long)uaddr;

		restart->arg1 = (unsigned long)val;

		restart->arg2 = (unsigned long)timed;

		restart->arg3 = abs_time;

		return -ERESTART_RESTARTBLOCK;

	}



 out_unlock_release_sem:

	queue_unlock(&q, hb);
@@ -1093,6 +1121,24 @@ static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time) 
	return ret;

}



static int futex_wait(u32 __user *uaddr, u32 val, unsigned long rel_time)

{

	int timed = (rel_time != MAX_SCHEDULE_TIMEOUT);

	return futex_wait_abstime(uaddr, val, timed, jiffies+rel_time);

}



static long futex_wait_restart(struct restart_block *restart)

{

	u32 __user *uaddr = (u32 __user *)restart->arg0;

	u32 val = (u32)restart->arg1;

	int timed = (int)restart->arg2;

	unsigned long abs_time = restart->arg3;



	restart->fn = do_no_restart_syscall;

	return (long)futex_wait_abstime(uaddr, val, timed, abs_time);

}





/*

 * Userspace tried a 0 -> TID atomic transition of the futex value

 * and failed. The kernel side here does the whole locking operation: