This is a note to let you know that I've just added the patch titled
SUNRPC: Prevent an rpc_task wakeup race
to the 3.4-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-prevent-an-rpc_task-wakeup-race.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f7b72b71fe00b5159d71f0d385c8d5e5865bcd32 Mon Sep 17 00:00:00 2001
From: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
Date: Wed, 22 May 2013 12:57:24 -0400
Subject: SUNRPC: Prevent an rpc_task wakeup race
From: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
commit a3c3cac5d31879cd9ae2de7874dc6544ca704aec upstream.
The lockless RPC_IS_QUEUED() test in __rpc_execute means that we need to
be careful about ordering the calls to rpc_test_and_set_running(task) and
rpc_clear_queued(task). If we get the order wrong, then we may end up
testing the RPC_TASK_RUNNING flag after __rpc_execute() has looped
and changed the state of the rpc_task.
Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Cc: Weng Meiling <wengmeiling.weng@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/sunrpc/sched.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -305,11 +305,17 @@ EXPORT_SYMBOL_GPL(__rpc_wait_for_complet
* Note: If the task is ASYNC, and is being made runnable after sitting on an
* rpc_wait_queue, this must be called with the queue spinlock held to protect
* the wait queue operation.
+ * Note the ordering of rpc_test_and_set_running() and rpc_clear_queued(),
+ * which is needed to ensure that __rpc_execute() doesn't loop (due to the
+ * lockless RPC_IS_QUEUED() test) before we've had a chance to test
+ * the RPC_TASK_RUNNING flag.
*/
static void rpc_make_runnable(struct rpc_task *task)
{
+ bool need_wakeup = !rpc_test_and_set_running(task);
+
rpc_clear_queued(task);
- if (rpc_test_and_set_running(task))
+ if (!need_wakeup)
return;
if (RPC_IS_ASYNC(task)) {
INIT_WORK(&task->u.tk_work, rpc_async_schedule);
Patches currently in stable-queue which might be from Trond.Myklebust@xxxxxxxxxx are
queue-3.4/sunrpc-clarify-comments-on-rpc_make_runnable.patch
queue-3.4/sunrpc-prevent-an-rpc_task-wakeup-race.patch
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