From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: [PATCH] block: eliminate potential for infinite loop in blkdev_issue_discard Date: Mon, 27 Sep 2010 14:13:22 -0400 Message-ID: <20100927181321.GC14180@redhat.com> References: <1285605664-27027-1-git-send-email-martin.petersen@oracle.com> <1285605664-27027-3-git-send-email-martin.petersen@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx1.redhat.com ([209.132.183.28]:56802 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751502Ab0I0SNc (ORCPT ); Mon, 27 Sep 2010 14:13:32 -0400 Content-Disposition: inline In-Reply-To: <1285605664-27027-3-git-send-email-martin.petersen@oracle.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: "Martin K. Petersen" Cc: jaxboe@fusionio.com, James.Bottomley@hansenpartnership.com, linux-scsi@vger.kernel.org, dm-devel@redhat.com Due to the recently identified overflow in read_capacity_16() it was possible for max_discard_sectors to be zero but still have discards enabled on the associated device's queue. Eliminate the possibility for blkdev_issue_discard to infinitely loop. Interestingly this issue wasn't identified until a device, whose discard_granularity was 0 due to read_capacity_16 overflow, was consumed by blk_stack_limits() to construct limits for a higher-level DM multipath device. The multipath device's resulting limits never had the discard limits stacked because blk_stack_limits() will only do so if the bottom device's discard_granularity != 0. This resulted in the multipath device's limits.max_discard_sectors being 0. Signed-off-by: Mike Snitzer --- block/blk-lib.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-) diff --git a/block/blk-lib.c b/block/blk-lib.c index c392029..186f249 100644 --- a/block/blk-lib.c +++ b/block/blk-lib.c @@ -56,7 +56,10 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector, * granularity */ max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9); - if (q->limits.discard_granularity) { + if (unlikely(!max_discard_sectors)) { + /* Avoid infinite loop (below) */ + return -EOPNOTSUPP; + } else if (q->limits.discard_granularity) { unsigned int disc_sects = q->limits.discard_granularity >> 9; max_discard_sectors &= ~(disc_sects - 1);