Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759785Ab2EWO60 (ORCPT ); Wed, 23 May 2012 10:58:26 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:51760 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754640Ab2EWO6Y (ORCPT ); Wed, 23 May 2012 10:58:24 -0400 Date: Wed, 23 May 2012 10:58:24 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Lin Ming cc: Jens Axboe , Jeff Moyer , , , Subject: Re: [RFC v2 PATCH 2/4] block: add queue runtime pm callbacks In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1532 Lines: 41 On Wed, 23 May 2012, Lin Ming wrote: > Let's consider below code. > > @@ -587,6 +591,11 @@ void __elv_add_request(struct request_queue *q, > struct request *rq, int where) > { > trace_block_rq_insert(q, rq); > > + if (!(rq->cmd_flags & REQ_PM)) > + if (q->nr_pending++ == 0 && (q->rpm_status == RPM_SUSPENDED || > + q->rpm_status == RPM_SUSPENDING) && q->dev) > + pm_request_resume(q->dev); > + > rq->q = q; > > if (rq->cmd_flags & REQ_SOFTBARRIER) { > > Block layer reads runtime status and pm core writes this status. > PM core uses dev->power.lock to protect this status. > > I was thinking will it have problem if block layer does not acquire > dev->power.lock? > From your explanation below, it seems does not have problem. I don't think it's a problem, because all you're doing is reading dev->power.rpm_status -- you're not writing it. On the other hand, there's nothing really wrong with keeping your own local copy of rpm_status. You could think of it as being the queue's status as opposed to the device's status. (Also, some people might argue that dev->power.rpm_status is supposed to be private to the runtime PM core and shouldn't be used by other code.) Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/