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Date: Fri, 7 Mar 2014 17:08:14 -0800 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Trond Myklebust <Trond.Myklebust@...app.com>, Ben Hutchings <ben@...adent.org.uk>, Weng Meiling <wengmeiling.weng@...wei.com> Subject: [PATCH 3.4 78/99] SUNRPC: Prevent an rpc_task wakeup race 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Trond Myklebust <Trond.Myklebust@...app.com> commit a3c3cac5d31879cd9ae2de7874dc6544ca704aec upstream. 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@...app.com> Signed-off-by: Ben Hutchings <ben@...adent.org.uk> Cc: Weng Meiling <wengmeiling.weng@...wei.com> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- net/sunrpc/sched.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -305,11 +305,17 @@ EXPORT_SYMBOL_GPL(__rpc_wait_for_complet * 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); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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