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SUNRPC: Prevent an rpc_task wakeup race

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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>
Cc: stable@vger.kernel.org
This commit is contained in:
Trond Myklebust 2013-05-22 12:57:24 -04:00
parent 774d5f14ee
commit a3c3cac5d3
1 changed files with 7 additions and 1 deletions
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8
net/sunrpc/sched.c
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@ -324,11 +324,17 @@ 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);