From: Nick Piggin This memory barrier is not needed because the waitqueue will only get waiters on it in the following situations: rq->count has exceeded the threshold - however all manipulations of ->count are performed under the runqueue lock, and so we will correctly pick up any waiter. Memory allocation for the request fails. In this case, there is no additional help provided by the memory barrier. We are guaranteed to eventually wake up waiters because the request allocation mempool guarantees that if the mem allocation for a request fails, there must be some requests in flight. They will wake up waiters when they are retired. Signed-off-by: Nick Piggin Cc: Jens Axboe Signed-off-by: Andrew Morton --- drivers/block/ll_rw_blk.c | 1 - 1 files changed, 1 deletion(-) diff -puN drivers/block/ll_rw_blk.c~blk-no-memory-barrier drivers/block/ll_rw_blk.c --- 25/drivers/block/ll_rw_blk.c~blk-no-memory-barrier 2005-05-03 20:53:50.000000000 -0700 +++ 25-akpm/drivers/block/ll_rw_blk.c 2005-05-03 20:53:50.000000000 -0700 @@ -1839,7 +1839,6 @@ static void __freed_request(request_queu clear_queue_congested(q, rw); if (rl->count[rw] + 1 <= q->nr_requests) { - smp_mb(); if (waitqueue_active(&rl->wait[rw])) wake_up(&rl->wait[rw]); _