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[3.5.y.z,extended,stable] Patch "SUNRPC: Prevent an rpc_task wakeup race" has been added to staging queue

Message ID 1369734687-7019-1-git-send-email-luis.henriques@canonical.com
State New
Headers show

Commit Message

Luis Henriques May 28, 2013, 9:51 a.m. UTC 
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@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@netapp.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 net/sunrpc/sched.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--
1.8.1.2
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Patch

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);