Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755082Ab0GAUP3 (ORCPT ); Thu, 1 Jul 2010 16:15:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58885 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752491Ab0GAUP2 (ORCPT ); Thu, 1 Jul 2010 16:15:28 -0400 Date: Thu, 1 Jul 2010 16:15:08 -0400 From: Mike Snitzer To: FUJITA Tomonori Cc: axboe@kernel.dk, hch@lst.de, James.Bottomley@suse.de, linux-scsi@vger.kernel.org, dm-devel@redhat.com, linux-kernel@vger.kernel.org Subject: Re: scsi: address leak in the error path of discard page allocation Message-ID: <20100701201508.GA28546@redhat.com> References: <1277981359-10717-1-git-send-email-fujita.tomonori@lab.ntt.co.jp> <1277981359-10717-3-git-send-email-fujita.tomonori@lab.ntt.co.jp> <20100701130328.GB19605@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100701130328.GB19605@redhat.com> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5213 Lines: 141 On Thu, Jul 01 2010 at 9:03am -0400, Mike Snitzer wrote: > On Thu, Jul 01 2010 at 6:49am -0400, > FUJITA Tomonori wrote: > > > This fixes discard page leak by using q->unprep_rq_fn facility. > > > > q->unprep_rq_fn is called when all the data buffer (req->bio and > > scsi_data_buffer) in the request is freed. > > > > sd_unprep() uses rq->buffer to free discard page allocated in > > sd_prepare_discard(). > > > > Signed-off-by: FUJITA Tomonori > > Thanks for sorting this out Tomo, all 3 patches work great! > > BTW, there is one remaining (rare) leak in the allocation path. > > The following patch serves to fix it but I'm not sure if there is a more > elegant way to address this. I've continued to look at this to arrive at alternative implementation. Here is a summary of the problem: A 'scsi_setup_discard_cmnd' return other than BLKPREP_OK will not cause a discard request to get completely stripped down ('blk_finish_request' isn't calling 'blk_unprep_request' because REQ_DONTPREP is not set by 'scsi_prep_return' for none BLKPREP_OK return). Therefore the discard request's page will _not_ get cleaned up. Aside from code inspection, I confirmed this by adding some test code to force a one-time initial BLKPREP_DEFER return from 'scsi_setup_discard_cmnd'. > An alternative would be to check if the page is already allocated > (before allocating the page in scsi_setup_discard_cmnd)? Unfortunatey this "alternative" won't work because it completely ignores the case where BLKPREP_KILL is returned from scsi_setup_discard_cmnd'. > Please advise, thanks. In short, I'm not too happy that the following patch doesn't allow for centralized cleanup of the discard request's page (via sd_unprep_fn). But in order to do that we'd likely have to: 1) relax blk_finish_request's REQ_DONTPREP constraint 2) add other weird conditionals within blk_unprep_request because the discard request wasn't _really_ prepared? So given this I'm inclined to stick with the following patch. Jens and/or James, what do you think? Mike > From: Mike Snitzer > Subject: scsi: address leak in the error path of discard page allocation > > Be sure to free the discard page if scsi_setup_blk_pc_cmnd fails. > E.g. Returning BLKPREP_DEFER from scsi_setup_blk_pc_cmnd will not cause > the request to be processed by sd_unprep_fn before the request is > retried (preparation included). > > Signed-off-by: Mike Snitzer > > --- > block/blk-core.c | 23 +++++++++++++++++++++++ > drivers/scsi/sd.c | 6 +++++- > include/linux/blkdev.h | 1 + > 3 files changed, 29 insertions(+), 1 deletion(-) > > Index: linux-2.6/drivers/scsi/sd.c > =================================================================== > --- linux-2.6.orig/drivers/scsi/sd.c > +++ linux-2.6/drivers/scsi/sd.c > @@ -466,7 +466,11 @@ static int scsi_setup_discard_cmnd(struc > > blk_add_request_payload(rq, page, len); > ret = scsi_setup_blk_pc_cmnd(sdp, rq); > - rq->buffer = page_address(page); > + if (ret != BLKPREP_OK) { > + blk_clear_request_payload(rq); > + __free_page(page); > + } else > + rq->buffer = page_address(page); > return ret; > } > > Index: linux-2.6/block/blk-core.c > =================================================================== > --- linux-2.6.orig/block/blk-core.c > +++ linux-2.6/block/blk-core.c > @@ -1164,6 +1164,29 @@ void blk_add_request_payload(struct requ > } > EXPORT_SYMBOL_GPL(blk_add_request_payload); > > +/** > + * blk_clear_request_payload - clear a request's payload > + * @rq: request to update > + * > + * The driver needs to take care of freeing the payload itself. > + */ > +void blk_clear_request_payload(struct request *rq) > +{ > + struct bio *bio = rq->bio; > + > + rq->__data_len = rq->resid_len = 0; > + rq->nr_phys_segments = 0; > + rq->buffer = NULL; > + > + bio->bi_size = 0; > + bio->bi_vcnt = 0; > + bio->bi_phys_segments = 0; > + > + bio->bi_io_vec->bv_page = NULL; > + bio->bi_io_vec->bv_len = 0; > +} > +EXPORT_SYMBOL_GPL(blk_clear_request_payload); > + > void init_request_from_bio(struct request *req, struct bio *bio) > { > req->cpu = bio->bi_comp_cpu; > Index: linux-2.6/include/linux/blkdev.h > =================================================================== > --- linux-2.6.orig/include/linux/blkdev.h > +++ linux-2.6/include/linux/blkdev.h > @@ -781,6 +781,7 @@ extern void blk_insert_request(struct re > extern void blk_requeue_request(struct request_queue *, struct request *); > extern void blk_add_request_payload(struct request *rq, struct page *page, > unsigned int len); > +extern void blk_clear_request_payload(struct request *rq); > extern int blk_rq_check_limits(struct request_queue *q, struct request *rq); > extern int blk_lld_busy(struct request_queue *q); > extern int blk_rq_prep_clone(struct request *rq, struct request *rq_src, -- 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/