dm: add two stage requeue mechanism
Commit 61b6e2e5 ("dm: fix BLK_STS_DM_REQUEUE handling when dm_io represents split bio") reverted DM core's bio splitting back to using bio_split()+bio_chain() because it was found that otherwise DM's BLK_STS_DM_REQUEUE would trigger a live-lock waiting for bio completion that would never occur. Restore using bio_trim()+bio_inc_remaining(), like was done in commit 7dd76d1f ("dm: improve bio splitting and associated IO accounting"), but this time with proper handling for the above scenario that is covered in more detail in the commit header for 61b6e2e5 . Solve this issue by adding a two staged dm_io requeue mechanism that uses the new dm_bio_rewind() via dm_io_rewind(): 1) requeue the dm_io into the requeue_list added to struct mapped_device, and schedule it via new added requeue work. This workqueue just clones the dm_io->orig_bio (which DM saves and ensures its end sector isn't modified). dm_io_rewind() uses the sectors and sectors_offset members of the dm_io that are recorded relative to the end of orig_bio: dm_bio_rewind()+bio_trim() are then used to make that cloned bio reflect the subset of the original bio that is represented by the dm_io that is being requeued. 2) the 2nd stage requeue is same with original requeue, but io->orig_bio points to new cloned bio (which matches the requeued dm_io as described above). This allows DM core to shift the need for bio cloning from bio-split time (during IO submission) to the less likely BLK_STS_DM_REQUEUE handling (after IO completes with that error). Signed-off-by:Ming Lei <ming.lei@redhat.com> Signed-off-by:
Mike Snitzer <snitzer@kernel.org>
parent
61cbe788
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