[ 03/56] SUNRPC: Add barriers to ensure read ordering in rpc_wake_up_task_queue_locked

Greg Kroah-Hartman
2013-04-02T22:50:35Z

From: Trond Myklebust <Trond.Myklebust@netapp.com>

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@netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/sunrpc/sched.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -135,6 +135,8 @@ 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",
@@ -369,8 +371,11 @@ 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);
+ }
}

/*