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Commit a3c3cac5d31879cd9ae2de7874dc6544ca704aec

Authored by Trond Myklebust
1 parent 774d5f14ee
Exists in smarc-l5.0.0_1.0.0-ga and in 5 other branches imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga

SUNRPC: Prevent an rpc_task wakeup race 

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

Showing 1 changed file with 7 additions and 1 deletions Side-by-side Diff

... ... @@ -324,11 +324,17 @@
324 324 * Note: If the task is ASYNC, and is being made runnable after sitting on an
325 325 * rpc_wait_queue, this must be called with the queue spinlock held to protect
326 326 * the wait queue operation.
  327 + * Note the ordering of rpc_test_and_set_running() and rpc_clear_queued(),
  328 + * which is needed to ensure that __rpc_execute() doesn't loop (due to the
  329 + * lockless RPC_IS_QUEUED() test) before we've had a chance to test
  330 + * the RPC_TASK_RUNNING flag.
327 331 */
328 332 static void rpc_make_runnable(struct rpc_task *task)
329 333 {
  334 + bool need_wakeup = !rpc_test_and_set_running(task);
  335 +
330 336 rpc_clear_queued(task);
331   - if (rpc_test_and_set_running(task))
  337 + if (!need_wakeup)
332 338 return;
333 339 if (RPC_IS_ASYNC(task)) {
334 340 INIT_WORK(&task->u.tk_work, rpc_async_schedule);