[PATCH 4.12 11/31] NFSv4.1: Fix a race where CB_NOTIFY_LOCK fails to wake a waiter

From: Greg Kroah-Hartman
Date: Thu Aug 03 2017 - 19:21:57 EST

4.12-stable review patch. If anyone has any objections, please let me know.


From: Benjamin Coddington <bcodding@xxxxxxxxxx>

commit b7dbcc0e433f0f61acb89ed9861ec996be4f2b38 upstream.

nfs4_retry_setlk() sets the task's state to TASK_INTERRUPTIBLE within the
same region protected by the wait_queue's lock after checking for a
notification from CB_NOTIFY_LOCK callback. However, after releasing that
lock, a wakeup for that task may race in before the call to
freezable_schedule_timeout_interruptible() and set TASK_WAKING, then
freezable_schedule_timeout_interruptible() will set the state back to
TASK_INTERRUPTIBLE before the task will sleep. The result is that the task
will sleep for the entire duration of the timeout.

Since we've already set TASK_INTERRUPTIBLE in the locked section, just use
freezable_schedule_timout() instead.

Fixes: a1d617d8f134 ("nfs: allow blocking locks to be awoken by lock callbacks")
Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

fs/nfs/nfs4proc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -6441,7 +6441,7 @@ nfs4_retry_setlk(struct nfs4_state *stat
spin_unlock_irqrestore(&q->lock, flags);

- freezable_schedule_timeout_interruptible(NFS4_LOCK_MAXTIMEOUT);
+ freezable_schedule_timeout(NFS4_LOCK_MAXTIMEOUT);

finish_wait(q, &wait);