Subject: Re: [dm-devel] [PATCH V15 00/18] block: support multi-page bvec
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>, 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
References: <20190215111324.30129-1-ming.lei@redhat.com>
 <c52b6a8b-d1d4-67ff-f81c-371d09cc6d5b@kernel.dk>
 <1550250855.31902.102.camel@acm.org> <20190217131128.GB7296@ming.t460p>
 <1550593699.31902.115.camel@acm.org> <20190220011719.GA13035@ming.t460p>
From:   Bart Van Assche <bvanassche@acm.org>
Message-ID: <8253d52d-a77a-b008-1fbd-f2f0a794a022@acm.org>
Date:   Tue, 19 Feb 2019 18:37:09 -0800
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On 2/19/19 5:17 PM, Ming Lei wrote:
> On Tue, Feb 19, 2019 at 08:28:19AM -0800, Bart Van Assche wrote:
>> With this patch applied test nvmeof-mp/002 fails as follows:
>>
>> [  694.700400] kernel BUG at lib/sg_pool.c:103!
>> [  694.705932] invalid opcode: 0000 [#1] PREEMPT SMP KASAN
>> [  694.708297] CPU: 2 PID: 349 Comm: kworker/2:1H Tainted: G    B             5.0.0-rc6-dbg+ #2
>> [  694.711730] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
>> [  694.715113] Workqueue: kblockd blk_mq_run_work_fn
>> [  694.716894] RIP: 0010:sg_alloc_table_chained+0xe5/0xf0
>> [  694.758222] Call Trace:
>> [  694.759645]  nvme_rdma_queue_rq+0x2aa/0xcc0 [nvme_rdma]
>> [  694.764915]  blk_mq_try_issue_directly+0x2a5/0x4b0
>> [  694.771779]  blk_insert_cloned_request+0x11e/0x1c0
>> [  694.778417]  dm_mq_queue_rq+0x3d1/0x770
>> [  694.793400]  blk_mq_dispatch_rq_list+0x5fc/0xb10
>> [  694.798386]  blk_mq_sched_dispatch_requests+0x2f7/0x300
>> [  694.803180]  __blk_mq_run_hw_queue+0xd6/0x180
>> [  694.808933]  blk_mq_run_work_fn+0x27/0x30
>> [  694.810315]  process_one_work+0x4f1/0xa40
>> [  694.813178]  worker_thread+0x67/0x5b0
>> [  694.814487]  kthread+0x1cf/0x1f0
>> [  694.819134]  ret_from_fork+0x24/0x30
>>
>> The code in sg_pool.c that triggers the BUG() statement is as follows:
>>
>> int sg_alloc_table_chained(struct sg_table *table, int nents,
>> 		struct scatterlist *first_chunk)
>> {
>> 	int ret;
>>
>> 	BUG_ON(!nents);
>> [ ... ]
>>
>> Bart.
> 
> I can reproduce this issue("kernel BUG at lib/sg_pool.c:103") without mp-bvec patches,
> so looks it isn't the fault of this patchset.

Thanks Ming for your feedback.

Jens, I don't see that issue with kernel v5.0-rc6. Does that mean that 
the sg_pool BUG() is a regression in your for-next branch that predates 
Ming's multi-page bvec patch series?

Thanks,

Bart.