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authorHou Tao <houtao1@huawei.com>2017-10-17 14:16:28 -0700
committerDarrick J. Wong <darrick.wong@oracle.com>2017-10-26 15:38:22 -0700
commit0bd89676c4fed53b003025bc4a5200861ac5d8ef (patch)
tree466a692aa4012845b76395f7d99954b5180bcf3e
parentf0387501652ed39f3bebc72e8a6b5abb405eb2b7 (diff)
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>
-rw-r--r--fs/xfs/xfs_trans_ail.c21
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);