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

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Date:   Tue, 19 Feb 2019 08:28:19 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Mike Snitzer <snitzer@...hat.com>,
        linux-mm@...ck.org, dm-devel@...hat.com,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Omar Sandoval <osandov@...com>, cluster-devel@...hat.com,
        linux-ext4@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...il.com>,
        Boaz Harrosh <ooo@...ctrozaur.com>,
        Gao Xiang <gaoxiang25@...wei.com>, Coly Li <colyli@...e.de>,
        linux-raid@...r.kernel.org, Bob Peterson <rpeterso@...hat.com>,
        linux-bcache@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Dave Chinner <dchinner@...hat.com>,
        David Sterba <dsterba@...e.com>, linux-block@...r.kernel.org,
        Theodore Ts'o <tytso@....edu>, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-btrfs@...r.kernel.org
Subject: Re: [dm-devel] [PATCH V15 00/18] block: support multi-page bvec

On Sun, 2019-02-17 at 21:11 +0800, Ming Lei wrote:
> The following patch should fix this issue:
> 
> 
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index bed065904677..066b66430523 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -363,13 +363,15 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
>  	struct bio_vec bv, bvprv = { NULL };
>  	int prev = 0;
>  	unsigned int seg_size, nr_phys_segs;
> -	unsigned front_seg_size = bio->bi_seg_front_size;
> +	unsigned front_seg_size;
>  	struct bio *fbio, *bbio;
>  	struct bvec_iter iter;
>  
>  	if (!bio)
>  		return 0;
>  
> +	front_seg_size = bio->bi_seg_front_size;
> +
>  	switch (bio_op(bio)) {
>  	case REQ_OP_DISCARD:
>  	case REQ_OP_SECURE_ERASE:

Hi Ming,

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.