Re: [dm-devel] [PATCH V15 00/18] block: support multi-page bvec

From: Bart Van Assche <bvanassche@acm.org>
To: Jens Axboe <axboe@kernel.dk>, Ming Lei <ming.lei@redhat.com>
Cc: Mike Snitzer <snitzer@redhat.com>,
	linux-mm@kvack.org, dm-devel@redhat.com,
	Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
	"Darrick J . Wong" <darrick.wong@oracle.com>,
	Omar Sandoval <osandov@fb.com>,
	cluster-devel@redhat.com, linux-ext4@vger.kernel.org,
	Kent Overstreet <kent.overstreet@gmail.com>,
	Boaz Harrosh <ooo@electrozaur.com>,
	Gao Xiang <gaoxiang25@huawei.com>, Coly Li <colyli@suse.de>,
	linux-raid@vger.kernel.org, Bob Peterson <rpeterso@redhat.com>,
	linux-bcache@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Dave Chinner <dchinner@redhat.com>,
	David Sterba <dsterba@suse.com>,
	linux-block@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>,
	linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org
Subject: Re: [dm-devel] [PATCH V15 00/18] block: support multi-page bvec
Date: Fri, 15 Feb 2019 09:14:15 -0800	[thread overview]
Message-ID: <1550250855.31902.102.camel@acm.org> (raw)
In-Reply-To: <c52b6a8b-d1d4-67ff-f81c-371d09cc6d5b@kernel.dk>

On Fri, 2019-02-15 at 08:49 -0700, Jens Axboe wrote:
> On 2/15/19 4:13 AM, Ming Lei wrote:
> > This patchset brings multi-page bvec into block layer:
> 
> Applied, thanks Ming. Let's hope it sticks!

Hi Jens and Ming,

Test nvmeof-mp/002 fails with Jens' for-next branch from this morning.
I have not yet tried to figure out which patch introduced the failure.
Anyway, this is what I see in the kernel log for test nvmeof-mp/002:

[  475.611363] BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
[  475.621188] #PF error: [normal kernel read fault]
[  475.623148] PGD 0 P4D 0  
[  475.624737] Oops: 0000 [#1] PREEMPT SMP KASAN
[  475.626628] CPU: 1 PID: 277 Comm: kworker/1:1H Tainted: G    B             5.0.0-rc6-dbg+ #1
[  475.630232] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[  475.633855] Workqueue: kblockd blk_mq_requeue_work
[  475.635777] RIP: 0010:__blk_recalc_rq_segments+0xbe/0x590
[  475.670948] Call Trace:
[  475.693515]  blk_recalc_rq_segments+0x2f/0x50
[  475.695081]  blk_insert_cloned_request+0xbb/0x1c0
[  475.701142]  dm_mq_queue_rq+0x3d1/0x770
[  475.707225]  blk_mq_dispatch_rq_list+0x5fc/0xb10
[  475.717137]  blk_mq_sched_dispatch_requests+0x256/0x300
[  475.721767]  __blk_mq_run_hw_queue+0xd6/0x180
[  475.725920]  __blk_mq_delay_run_hw_queue+0x25c/0x290
[  475.727480]  blk_mq_run_hw_queue+0x119/0x1b0
[  475.732019]  blk_mq_run_hw_queues+0x7b/0xa0
[  475.733468]  blk_mq_requeue_work+0x2cb/0x300
[  475.736473]  process_one_work+0x4f1/0xa40
[  475.739424]  worker_thread+0x67/0x5b0
[  475.741751]  kthread+0x1cf/0x1f0
[  475.746034]  ret_from_fork+0x24/0x30

(gdb) list *(__blk_recalc_rq_segments+0xbe)
0xffffffff816a152e is in __blk_recalc_rq_segments (block/blk-merge.c:366).
361                                                  struct bio *bio)
362     {
363             struct bio_vec bv, bvprv = { NULL };
364             int prev = 0;
365             unsigned int seg_size, nr_phys_segs;
366             unsigned front_seg_size = bio->bi_seg_front_size;
367             struct bio *fbio, *bbio;
368             struct bvec_iter iter;
369
370             if (!bio)

Bart.