| Message ID | 4c1c7cd404173b9888464a2d7e2a430cc7e18737.1720643005.git.bcodding@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | A rare failure to wake up sync tasks | expand |
diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c index 6debf4fd42d4..34b31be75497 100644 --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -369,8 +369,11 @@ 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 { + /* paired with set_current_state() in prepare_to_wait */ + smp_mb(); wake_up_bit(&task->tk_runstate, RPC_TASK_QUEUED); + } } /*
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() before the wake_up_bit(), which pairs with prepare_to_wait() calling set_current_state(). Signed-off-by: Benjamin Coddington <bcodding@redhat.com> --- net/sunrpc/sched.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)