Re: [jet.chen@xxxxxxxxx: [bio] kernel BUG at drivers/block/virtio_blk.c:166!]

[Ming Lei]

On Tue, May 27, 2014 at 3:43 AM, Maurizio Lombardi <mlombard@xxxxxxxxxx> wrote:
> Hi Jens,
>
> looks like that commit 3979ef4dcf3d1de55a560a3a4016c30a835df44d ("bio-modify-__bio_add_page-to-accept-pages-that-dont-start-a-new-segment-v3")
> introduces a regression, as reported by Jet Chan.
>
> Do you have any idea about the possible problem with this patch?
>
> it is the one that performs a recount of the segments in case of failure in __bio_add_page()
>
> http://www.spinics.net/lists/mm-commits/msg103684.html
>
> I would not be surprised if the bug was introduced by fceb38f36f, because it
> contained a mystake that commit 3979ef4dcf supposedly fixed.
> But learning that commit 3979ef4dcf is introducing a regression leaves
> me quite puzzled.

>From code of __blk_recalc_rq_segments(), looks it
won't check if recounted physical segment number is
bigger than queue_max_segments(), so wondering if
blk_recount_segments() can always decrease
physical segment number.

Thanks,
--
Ming Lei
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