From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:44900 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750737AbdLMW5M (ORCPT ); Wed, 13 Dec 2017 17:57:12 -0500 Date: Wed, 13 Dec 2017 17:57:08 -0500 From: Mike Snitzer To: Bart Van Assche Cc: dm-devel@redhat.com, Elena Reshetova , Kees Cook , David Windsor , Hans Liljestrand , Hannes Reinecke , stable@vger.kernel.org Subject: Re: dm: Fix a recently introduced reference counting bug Message-ID: <20171213225708.GA6507@redhat.com> References: <20171213214618.21767-1-bart.vanassche@wdc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171213214618.21767-1-bart.vanassche@wdc.com> Sender: stable-owner@vger.kernel.org List-ID: On Wed, Dec 13 2017 at 4:46pm -0500, Bart Van Assche wrote: > This patch avoids that the following message occurs sporadically > in the system log (revealing that pgpath->path.dev->name became > a dangling pointer): > > device-mapper: table: 254:2: device kkkkkkkkkkkkkkkkkkk?????????x0?a?????E??????????????E??????F?????2?????pF??????PF?????9[F??????]F???????#???????#??????'f????? not in table devices list > > This patch also fixes the following kernel crash: > > general protection fault: 0000 [#1] PREEMPT SMP > RIP: 0010:multipath_busy+0x77/0xd0 [dm_multipath] > Call Trace: > dm_mq_queue_rq+0x44/0x110 [dm_mod] > blk_mq_dispatch_rq_list+0x73/0x440 > blk_mq_do_dispatch_sched+0x60/0xe0 > blk_mq_sched_dispatch_requests+0x11a/0x1a0 > __blk_mq_run_hw_queue+0x11f/0x1c0 > __blk_mq_delay_run_hw_queue+0x95/0xe0 > blk_mq_run_hw_queue+0x25/0x80 > blk_mq_flush_plug_list+0x197/0x420 > blk_flush_plug_list+0xe4/0x270 > blk_finish_plug+0x27/0x40 > __do_page_cache_readahead+0x2b4/0x370 > force_page_cache_readahead+0xb4/0x110 > generic_file_read_iter+0x755/0x970 > __vfs_read+0xd2/0x140 > vfs_read+0x9b/0x140 > SyS_read+0x45/0xa0 > do_syscall_64+0x56/0x1a0 > entry_SYSCALL64_slow_path+0x25/0x25 > > From the disassembly of multipath_busy (0x77 = 119): > > ./include/linux/blkdev.h: > 992 return bdev->bd_disk->queue; /* this is never NULL */ > 0x00000000000006b4 <+116>: mov (%rax),%rax > 0x00000000000006b7 <+119>: mov 0xe0(%rax),%rax > > Fixes: commit 2a0b4682e09d ("dm: convert dm_dev_internal.count from atomic_t to refcount_t") > Signed-off-by: Bart Van Assche > Cc: Elena Reshetova > Cc: Kees Cook > Cc: David Windsor > Cc: Hans Liljestrand > Cc: Hannes Reinecke > Cc: stable@vger.kernel.org # v4.15 > --- > drivers/md/dm-table.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c > index 88130b5d95f9..ee5c389e7256 100644 > --- a/drivers/md/dm-table.c > +++ b/drivers/md/dm-table.c > @@ -459,6 +459,8 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode, > if (r) > return r; > refcount_inc(&dd->count); > + } else { > + refcount_inc(&dd->count); > } > > *result = dd->dm_dev; > -- > 2.15.1 > I've had a fix for this staged in linux-next for a while. Will be sending it to Linus tomorrow, see: https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-4.15&id=afc567a4977b2d798e05153dd131a3c8d4758c0c BTW, there was no need to cc: stable given that it'll get fixed in 4.15 (issue was introduced during the 4.15 merge). Mike