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Commit7dd76d1fee("dm: improve bio splitting and associated IO accounting") removed using cloned bio when dm io splitting is needed. Using bio_trim()+bio_inc_remaining() rather than bio_split()+bio_chain() causes multiple dm_io instances to share the same original bio, and it works fine if IOs are completed successfully. But a regression was caused for the case when BLK_STS_DM_REQUEUE is returned from any one of DM's cloned bios (whose dm_io share the same orig_bio). In this BLK_STS_DM_REQUEUE case only the mapped subset of the original bio for the current exact dm_io needs to be re-submitted. However, since the original bio is shared among all dm_io instances, the ->orig_bio actually only represents the last dm_io instance, so requeue can't work as expected. Also when more than one dm_io is requeued, the same original bio is requeued from all dm_io's completion handler, then race is caused. Fix this issue by still allocating one clone bio for completing io only, then io accounting can rely on ->orig_bio being unmodified. This is needed because the dm_io's sector_offset and sectors members are recorded relative to an unmodified ->orig_bio. In the future, we can go back to using bio_trim()+bio_inc_remaining() for dm's io splitting but then delay needing a bio clone only when handling BLK_STS_DM_REQUEUE, but that approach is a bit complicated (so it needs a development cycle): 1) bio clone needs to be done in task context 2) a block interface for unwinding bio is required Fixes:7dd76d1fee("dm: improve bio splitting and associated IO accounting") Reported-by: Benjamin Marzinski <bmarzins@redhat.com> Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
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