This is a note to let you know that I've just added the patch titled
SUNRPC: Fix a race to wake a sync task
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sunrpc-fix-a-race-to-wake-a-sync-task.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit bc5c75d2572217d6c2172157e14058c1e89d5727
Author: Benjamin Coddington <bcodding@xxxxxxxxxx>
Date: Wed Jul 17 10:49:33 2024 -0400
SUNRPC: Fix a race to wake a sync task
[ Upstream commit ed0172af5d6fc07d1b40ca82f5ca3979300369f7 ]
We've observed NFS clients with sync tasks sleeping in __rpc_execute
waiting on RPC_TASK_QUEUED that have not responded to a wake-up from
rpc_make_runnable(). I suspect this problem usually goes unnoticed,
because on a busy client the task will eventually be re-awoken by another
task completion or xprt event. However, if the state manager is draining
the slot table, a sync task missing a wake-up can result in a hung client.
We've been able to prove that the waker in rpc_make_runnable() successfully
calls wake_up_bit() (ie- there's no race to tk_runstate), but the
wake_up_bit() call fails to wake the waiter. I suspect the waker is
missing the load of the bit's wait_queue_head, so waitqueue_active() is
false. There are some very helpful comments about this problem above
wake_up_bit(), prepare_to_wait(), and waitqueue_active().
Fix this by inserting smp_mb__after_atomic() before the wake_up_bit(),
which pairs with prepare_to_wait() calling set_current_state().
Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index 9af919364a001..92d88aa62085b 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -349,8 +349,10 @@ static void rpc_make_runnable(struct workqueue_struct *wq,
if (RPC_IS_ASYNC(task)) {
INIT_WORK(&task->u.tk_work, rpc_async_schedule);
queue_work(wq, &task->u.tk_work);
- } else
+ } else {
+ smp_mb__after_atomic();
wake_up_bit(&task->tk_runstate, RPC_TASK_QUEUED);
+ }
}
/*
