3.2.43-rc1 review patch. If anyone has any objections, please let me know.
------------------
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: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
net/sunrpc/sched.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -139,6 +139,8 @@ 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",
@@ -389,8 +391,11 @@ 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);
+ }
}
/*
--
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