Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754024Ab1CYPlX (ORCPT ); Fri, 25 Mar 2011 11:41:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:61606 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753757Ab1CYPlW (ORCPT ); Fri, 25 Mar 2011 11:41:22 -0400 Date: Fri, 25 Mar 2011 11:40:46 -0400 From: Mike Snitzer To: Markus Trippelsdorf Cc: Sergey Senozhatsky , Jens Axboe , linux-kernel@vger.kernel.org, Chris Mason , tj@kernel.org, Vivek Goyal , Jeff Moyer Subject: Re: elevator private data for REQ_FLUSH Message-ID: <20110325154024.GA16029@redhat.com> References: <20110325151530.GA4414@swordfish.minsk.epam.com> <20110325152228.GA1707@gentoo.trippels.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110325152228.GA1707@gentoo.trippels.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3065 Lines: 72 On Fri, Mar 25 2011 at 11:22am -0400, Markus Trippelsdorf wrote: > On 2011.03.25 at 17:15 +0200, Sergey Senozhatsky wrote: > > Hello, > > > > Commit > > 9d5a4e946ce5352f19400b6370f4cd8e72806278 > > block: skip elevator data initialization for flush requests > > > > Skip elevator initialization for flush requests by passing priv=0 to > > blk_alloc_request() in get_request(). As such elv_set_request() is > > never called for flush requests. > > > > introduced priv flag, to skip elevator_private data init for FLUSH requests. > > This, I guess, lead to NULL pointer deref on my machine in cfq_insert_request, > > which requires elevator_private to be set: > > > > 1 [ 78.982169] Call Trace: > > 2 [ 78.982178] [] cfq_insert_request+0x4e/0x47d > > 3 [ 78.982184] [] ? do_raw_spin_lock+0x6b/0x122 > > > Should we in that case use ELEVATOR_INSERT_FLUSH for REQ_FLUSH | REQ_FUA requests > > (like below)? > > > > --- > > > > block/elevator.c | 2 ++ > > 1 files changed, 2 insertions(+), 0 deletions(-) > > > > diff --git a/block/elevator.c b/block/elevator.c > > index c387d31..b17e577 100644 > > --- a/block/elevator.c > > +++ b/block/elevator.c > > @@ -734,6 +734,8 @@ void __elv_add_request(struct request_queue *q, struct request *rq, int where) > > q->end_sector = rq_end_sector(rq); > > q->boundary_rq = rq; > > } > > + } else if (rq->cmd_flags & (REQ_FLUSH | REQ_FUA)) { > > + where = ELEVATOR_INSERT_FLUSH; > > } else if (!(rq->cmd_flags & REQ_ELVPRIV) && > > where == ELEVATOR_INSERT_SORT) > > where = ELEVATOR_INSERT_BACK; > > Thanks. That solves all (corruption-) problems that I reported earlier in an other > thread. So the flush-merge changes introduced ELEVATOR_INSERT_FLUSH (via commit ae1b1539). And the flush bio will now get ELEVATOR_INSERT_FLUSH in __make_request(). So it is interesting that the flush is getting inserted in the elevator at all. AFAIK that shouldn't be (and historically hasn't been) the case. Combination of onstack plug changes? 1 [ 78.982169] Call Trace: 2 [ 78.982178] [] cfq_insert_request+0x4e/0x47d 3 [ 78.982184] [] ? do_raw_spin_lock+0x6b/0x122 4 [ 78.982189] [] elv_insert+0x212/0x265 5 [ 78.982192] [] __elv_add_request+0x50/0x52 6 [ 78.982195] [] flush_plug_list+0xce/0x12f 7 [ 78.982199] [] __blk_flush_plug+0x15/0x21 8 [ 78.982205] [] schedule+0x43e/0xbea Mike -- 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/