diff options
| author | Benjamin Coddington <bcodding@redhat.com> | 2024-07-17 10:49:33 -0400 |
|---|---|---|
| committer | Anna Schumaker <Anna.Schumaker@Netapp.com> | 2024-07-18 10:49:12 -0400 |
| commit | ed0172af5d6fc07d1b40ca82f5ca3979300369f7 (patch) | |
| tree | 3e5a6279f1293da3e2a70f33a2933428fafeda07 /net/sunrpc/sched.c | |
| parent | a308996ed7c02d1cd6504ce73436ef3f1c1c75c0 (diff) | |
SUNRPC: Fix a race to wake a sync task
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@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Diffstat (limited to 'net/sunrpc/sched.c')
| -rw-r--r-- | net/sunrpc/sched.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c index 6debf4fd42d4..cef623ea1506 100644 --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -369,8 +369,10 @@ 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); + } } /* |