From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [PATCH] block: Make blk_drain_queue() work for stopped queues Date: Sun, 18 Mar 2012 19:47:47 +0000 Message-ID: <4F663BE3.4000503@acm.org> References: <4F65E09D.6010600@acm.org> <20120318155703.GB8045@dhcp-172-17-108-109.mtv.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from relay02ant.iops.be ([212.53.4.35]:41721 "EHLO relay02ant.iops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756381Ab2CRTrw (ORCPT ); Sun, 18 Mar 2012 15:47:52 -0400 In-Reply-To: <20120318155703.GB8045@dhcp-172-17-108-109.mtv.corp.google.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Tejun Heo Cc: Jens Axboe , Stanislaw Gruszka , linux-scsi On 03/18/12 15:57, Tejun Heo wrote: > On Sun, Mar 18, 2012 at 01:18:21PM +0000, Bart Van Assche wrote: >> All queued requests must be processed eventually. Hence make sure >> that blk_drain_queue() drains the queue even if the queue is in the >> stopped state. This patch makes it safe to invoke blk_cleanup_queue() >> on a stopped queue. > ... >> diff --git a/block/blk-core.c b/block/blk-core.c >> index 3a78b00..bdcec86 100644 >> --- a/block/blk-core.c >> +++ b/block/blk-core.c >> @@ -300,10 +300,8 @@ EXPORT_SYMBOL(blk_sync_queue); >> */ >> void __blk_run_queue(struct request_queue *q) >> { >> - if (unlikely(blk_queue_stopped(q))) >> - return; >> - >> - q->request_fn(q); >> + if (!blk_queue_stopped(q) || blk_queue_dead(q)) >> + q->request_fn(q); > So, this allows calling request_fn for dead && stopped queue. Have > you seen something which requires this? Not servicing queued SCSI requests can e.g. cause user space processes to hang. See also http://lkml.org/lkml/2011/8/27/6 for an example. Hence commit 3308511c93e6ad0d3c58984ecd6e5e57f96b12c8 which causes pending SCSI commands to be killed just before blk_cleanup_queue() is invoked. However, there is still a tiny race window left by that patch - new requests can get queued after the SCSI request function has been invoked by scsi_free_queue() and before blk_cleanup_queue() gets invoked. Hence the proposal to change the block layer to make sure that all queued requests get processed eventually. Bart.