[ 3.5.y.z extended stable ] Patch "SUNRPC: Prevent an rpc_task wakeup race" has been added to staging queue
Luis Henriques
luis.henriques at canonical.com
Tue May 28 09:51:27 UTC 2013
This is a note to let you know that I have just added a patch titled
SUNRPC: Prevent an rpc_task wakeup race
to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree
which can be found at:
http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Luis
------
>From 1b40481d805ca62449a737750154ec5c7b02443f Mon Sep 17 00:00:00 2001
From: Trond Myklebust <Trond.Myklebust at netapp.com>
Date: Wed, 22 May 2013 12:57:24 -0400
Subject: [PATCH] SUNRPC: Prevent an rpc_task wakeup race
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 at netapp.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
net/sunrpc/sched.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index 38cca32..c393017 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -305,11 +305,17 @@ EXPORT_SYMBOL_GPL(__rpc_wait_for_completion_task);
* 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);
--
1.8.1.2
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