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H A D | xfs_trans_ail.c | 0bd89676 Tue Oct 17 16:16:28 CDT 2017 Hou Tao <houtao1@huawei.com> 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> 0bd89676 Tue Oct 17 16:16:28 CDT 2017 Hou Tao <houtao1@huawei.com> 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>
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