On Tue, 2011-02-15 at 18:47 -0500, Trond Myklebust wrote:
> diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
> index 243fc09..11b71b1 100644
> --- a/net/sunrpc/sched.c
> +++ b/net/sunrpc/sched.c
> @@ -252,23 +252,39 @@ static void rpc_set_active(struct rpc_task *task)
>
> /*
> * Mark an RPC call as having completed by clearing the 'active' bit
> + * and then waking up all tasks that were sleeping.
> */
> -static void rpc_mark_complete_task(struct rpc_task *task)
> +static int rpc_complete_task(struct rpc_task *task)
> {
> - smp_mb__before_clear_bit();
> + void *m = &task->tk_runstate;
> + wait_queue_head_t *wq = bit_waitqueue(m, RPC_TASK_ACTIVE);
> + struct wait_bit_key k = __WAIT_BIT_KEY_INITIALIZER(m, RPC_TASK_ACTIVE);
> + unsigned long flags;
> + int ret;
> +
> + spin_lock_irqsave(&wq->lock, flags);
> clear_bit(RPC_TASK_ACTIVE, &task->tk_runstate);
> - smp_mb__after_clear_bit();
> - wake_up_bit(&task->tk_runstate, RPC_TASK_ACTIVE);
> + if (waitqueue_active(wq))
> + __wake_up_locked_key(wq, TASK_NORMAL, &k);
> + ret = atomic_dec_and_test(&task->tk_count);
> + spin_unlock_irqrestore(&wq->lock, flags);
> + return ret;
> }
>
> /*
> * Allow callers to wait for completion of an RPC call
> + *
> + * Note the use of out_of_line_wait_on_bit() rather than wait_on_bit()
> + * to enforce taking of the wq->lock and hence avoid races with
> + * rpc_complete_task().
> */
> int __rpc_wait_for_completion_task(struct rpc_task *task, int (*action)(void *))
> {
> + BUG_ON(!RPC_IS_ASYNC(task));
> +
> if (action == NULL)
> action = rpc_wait_bit_killable;
> - return wait_on_bit(&task->tk_runstate, RPC_TASK_ACTIVE,
> + return out_of_line_wait_on_bit(&task->tk_runstate, RPC_TASK_ACTIVE,
> action, TASK_KILLABLE);
> }
> EXPORT_SYMBOL_GPL(__rpc_wait_for_completion_task);
Never mind. The above ordering scheme is broken by the fact that
'wake_bit_function' calls autoremove_wake_function, which again means
that finish_wait optimises away the spin lock.
Back to the drawing board...
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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