[dm-devel] [PATCH] dm integrity: reinitialize __bi_remaining when reusing bio

[Daniel Glöckner]

Hello Christoph,

Am 02/25/20 um 20:12 schrieb Christoph Hellwig:
> On Tue, Feb 25, 2020 at 06:07:44PM +0100, Daniel Glöckner wrote:
>> In cases where dec_in_flight has to requeue the integrity_bio_wait work
>> to transfer the rest of the data, the __bi_remaining field of the bio
>> might already have been decremented to zero. Reusing the bio without
>> reinitializing that counter to 1 can then result in integrity_end_io
>> being called too early when the BIO_CHAIN flag is set, f.ex. due to
>> blk_queue_split. In our case this triggered the BUG() in
>> blk_mq_end_request when the hardware signalled completion of the bio
>> after integrity_end_io had modified it.
>>
>> Signed-off-by: Daniel Glöckner <dg at emlix.com>
> 
> Drivers have no business poking into these internals.  If a bio is
> reused the caller needs to use bio_reset instead.

bio_reset will reset too many fields. As you can see in the context of
the diff, dm-integrity expects f.ex. the values modified by bio_advance
to stay intact and the transfer should of course use the same disk and
operation.

How about doing the atomic_set in bio_remaining_done (in block/bio.c)
where the BIO_CHAIN flag is cleared once __bi_remaining hits zero?
Or is requeuing a bio without bio_reset really a no-go? In that case a
one-liner won't do...

Best regards,

  Daniel

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