From 0bd89676c4fed53b003025bc4a5200861ac5d8ef Mon Sep 17 00:00:00 2001 From: Hou Tao Date: Tue, 17 Oct 2017 14:16:28 -0700 Subject: [PATCH] xfs: check kthread_should_stop() after the setting of task state A umount hang is possible when a race occurs between the umount process and the xfsaild kthread. The following sequences outline the race: xfsaild: kthread_should_stop() => return false, so xfsaild continue umount: set_bit(KTHREAD_SHOULD_STOP, &kthread->flags) => by kthread_stop() umount: wake_up_process() => because xfsaild is still running, so 0 is returned xfsaild: __set_current_state(TASK_INTERRUPTIBLE) xfsaild: schedule() => now, xfsaild will wait indefinitely umount: wait_for_completion() => and umount will hang To fix that, we need to check kthread_should_stop() after we set the task state, so the xfsaild will either see the stop bit and exit or the task state is reset to runnable by wake_up_process() such that it isn't scheduled out indefinitely and detects the stop bit at the next iteration. Reviewed-by: Christoph Hellwig Reviewed-by: Brian Foster Signed-off-by: Hou Tao Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong --- fs/xfs/xfs_trans_ail.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c index 354368a906e5..4b1669f9d2b2 100644 --- a/fs/xfs/xfs_trans_ail.c +++ b/fs/xfs/xfs_trans_ail.c @@ -514,11 +514,26 @@ xfsaild( current->flags |= PF_MEMALLOC; set_freezable(); - while (!kthread_should_stop()) { + while (1) { if (tout && tout <= 20) - __set_current_state(TASK_KILLABLE); + set_current_state(TASK_KILLABLE); else - __set_current_state(TASK_INTERRUPTIBLE); + set_current_state(TASK_INTERRUPTIBLE); + + /* + * Check kthread_should_stop() after we set the task state + * to guarantee that we either see the stop bit and exit or + * the task state is reset to runnable such that it's not + * scheduled out indefinitely and detects the stop bit at + * next iteration. + * + * A memory barrier is included in above task state set to + * serialize again kthread_stop(). + */ + if (kthread_should_stop()) { + __set_current_state(TASK_RUNNING); + break; + } spin_lock(&ailp->xa_lock); -- GitLab