Re: dm: do not replace bioset for request-based dm

[Mike Snitzer <snitzer@redhat.com>]

On Mon, Feb 25 2013 at 11:49pm -0500,
Jun'ichi Nomura <j-nomura@ce.jp.nec.com> wrote:

> This patch fixes a regression introduced in v3.8, which causes oops
> like this when dm-multipath is used:
> 
> general protection fault: 0000 [#1] SMP
> RIP: 0010:[<ffffffff810fe754>]  [<ffffffff810fe754>] mempool_free+0x24/0xb0
> Call Trace:
>   <IRQ>
>   [<ffffffff81187417>] bio_put+0x97/0xc0
>   [<ffffffffa02247a5>] end_clone_bio+0x35/0x90 [dm_mod]
>   [<ffffffff81185efd>] bio_endio+0x1d/0x30
>   [<ffffffff811f03a3>] req_bio_endio.isra.51+0xa3/0xe0
>   [<ffffffff811f2f68>] blk_update_request+0x118/0x520
>   [<ffffffff811f3397>] blk_update_bidi_request+0x27/0xa0
>   [<ffffffff811f343c>] blk_end_bidi_request+0x2c/0x80
>   [<ffffffff811f34d0>] blk_end_request+0x10/0x20
>   [<ffffffffa000b32b>] scsi_io_completion+0xfb/0x6c0 [scsi_mod]
>   [<ffffffffa000107d>] scsi_finish_command+0xbd/0x120 [scsi_mod]
>   [<ffffffffa000b12f>] scsi_softirq_done+0x13f/0x160 [scsi_mod]
>   [<ffffffff811f9fd0>] blk_done_softirq+0x80/0xa0
>   [<ffffffff81044551>] __do_softirq+0xf1/0x250
>   [<ffffffff8142ee8c>] call_softirq+0x1c/0x30
>   [<ffffffff8100420d>] do_softirq+0x8d/0xc0
>   [<ffffffff81044885>] irq_exit+0xd5/0xe0
>   [<ffffffff8142f3e3>] do_IRQ+0x63/0xe0
>   [<ffffffff814257af>] common_interrupt+0x6f/0x6f
>   <EOI>
>   [<ffffffffa021737c>] srp_queuecommand+0x8c/0xcb0 [ib_srp]
>   [<ffffffffa0002f18>] scsi_dispatch_cmd+0x148/0x310 [scsi_mod]
>   [<ffffffffa000a38e>] scsi_request_fn+0x31e/0x520 [scsi_mod]
>   [<ffffffff811f1e57>] __blk_run_queue+0x37/0x50
>   [<ffffffff811f1f69>] blk_delay_work+0x29/0x40
>   [<ffffffff81059003>] process_one_work+0x1c3/0x5c0
>   [<ffffffff8105b22e>] worker_thread+0x15e/0x440
>   [<ffffffff8106164b>] kthread+0xdb/0xe0
>   [<ffffffff8142db9c>] ret_from_fork+0x7c/0xb0
> 
> The regression was introduced by the change
> c0820cf5 "dm: introduce per_bio_data", where dm started to replace
> bioset during table replacement.
> For bio-based dm, it is good because clone bios do not exist during the
> table replacement.
> For request-based dm, however, (not-yet-mapped) clone bios may stay in
> request queue and survive during the table replacement.
> So freeing the old bioset could cause the oops in bio_put().
> 
> Since the size of front_pad may change only with bio-based dm,
> it is not necessary to replace bioset for request-based dm.
> 
> Reported-by: Bart Van Assche <bvanassche@acm.org>
> Tested-by: Bart Van Assche <bvanassche@acm.org>
> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
> Cc: Alasdair G Kergon <agk@redhat.com>
> Cc: Mikulas Patocka <mpatocka@redhat.com>
> Cc: Mike Snitzer <snitzer@redhat.com>
> Cc: <stable@vger.kernel.org>

Acked-by: Mike Snitzer <snitzer@redhat.com>