This is a note to let you know that I've just added the patch titled
SUNRPC: Add barriers to ensure read ordering in rpc_wake_up_task_queue_locked
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-add-barriers-to-ensure-read-ordering-in-rpc_wake_up_task_queue_locked.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 1166fde6a923c30f4351515b6a9a1efc513e7d00 Mon Sep 17 00:00:00 2001
From: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
Date: Mon, 25 Mar 2013 11:23:40 -0400
Subject: SUNRPC: Add barriers to ensure read ordering in rpc_wake_up_task_queue_locked
From: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
commit 1166fde6a923c30f4351515b6a9a1efc513e7d00 upstream.
We need to be careful when testing task->tk_waitqueue in
rpc_wake_up_task_queue_locked, because it can be changed while we
are holding the queue->lock.
By adding appropriate memory barriers, we can ensure that it is safe to
test task->tk_waitqueue for equality if the RPC_TASK_QUEUED bit is set.
Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/sunrpc/sched.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -143,6 +143,8 @@ static void __rpc_add_wait_queue(struct
list_add_tail(&task->u.tk_wait.list, &queue->tasks[0]);
task->tk_waitqueue = queue;
queue->qlen++;
+ /* barrier matches the read in rpc_wake_up_task_queue_locked() */
+ smp_wmb();
rpc_set_queued(task);
dprintk("RPC: %5u added to queue %p \"%s\"\n",
@@ -399,8 +401,11 @@ static void __rpc_do_wake_up_task(struct
*/
static void rpc_wake_up_task_queue_locked(struct rpc_wait_queue *queue, struct rpc_task *task)
{
- if (RPC_IS_QUEUED(task) && task->tk_waitqueue == queue)
- __rpc_do_wake_up_task(queue, task);
+ if (RPC_IS_QUEUED(task)) {
+ smp_rmb();
+ if (task->tk_waitqueue == queue)
+ __rpc_do_wake_up_task(queue, task);
+ }
}
/*
Patches currently in stable-queue which might be from Trond.Myklebust@xxxxxxxxxx are
queue-3.4/sunrpc-add-barriers-to-ensure-read-ordering-in-rpc_wake_up_task_queue_locked.patch
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