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author | Hou Tao <houtao1@huawei.com> | 2017-10-17 14:16:28 -0700 |
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committer | Darrick J. Wong <darrick.wong@oracle.com> | 2017-10-26 15:38:22 -0700 |
commit | 0bd89676c4fed53b003025bc4a5200861ac5d8ef (patch) | |
tree | 466a692aa4012845b76395f7d99954b5180bcf3e /fs/xfs/xfs_trans_ail.c | |
parent | f0387501652ed39f3bebc72e8a6b5abb405eb2b7 (diff) | |
download | linux-stable-0bd89676c4fed53b003025bc4a5200861ac5d8ef.tar.gz linux-stable-0bd89676c4fed53b003025bc4a5200861ac5d8ef.tar.bz2 linux-stable-0bd89676c4fed53b003025bc4a5200861ac5d8ef.zip |
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 <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Diffstat (limited to 'fs/xfs/xfs_trans_ail.c')
-rw-r--r-- | fs/xfs/xfs_trans_ail.c | 21 |
1 files 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); |