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Btrfs: do not cache rbio pages if using raid6 recover

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Since raid6 recover tries all possible combinations of failed stripes,

- when raid6 rebuild algorithm is used, i.e. raid6_datap_recov() and
  raid6_2data_recov(), it may change the in-memory content of failed
  stripes, if such a raid bio is cached, a later raid write rmw or recover
  can steal @stripe_pages from it instead of reading from disks, such that
  it carries the wrong content to do write rmw or recovery and ends up
  with corruption or recovery failures.

- when raid5 rebuild algorithm is used, i.e. xor, raid bio can be cached
  because the only failed stripe which contains @rbio->bio_pages gets
  modified, others remain the same so that their in-memory content is
  consistent with their on-disk content.

This adds a check to skip caching rbio if using raid6 recover.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Liu Bo 2018-01-12 18:07:02 -07:00 committed by David Sterba
parent 0198e5b707
commit 44ac474def
1 changed files with 16 additions and 1 deletions
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17
fs/btrfs/raid56.c
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@ -1974,7 +1974,22 @@ cleanup:
cleanup_io:
if (rbio->operation == BTRFS_RBIO_READ_REBUILD) {
if (err == BLK_STS_OK)
/*
* - In case of two failures, where rbio->failb != -1:
*
* Do not cache this rbio since the above read reconstruction
* (raid6_datap_recov() or raid6_2data_recov()) may have
* changed some content of stripes which are not identical to
* on-disk content any more, otherwise, a later write/recover
* may steal stripe_pages from this rbio and end up with
* corruptions or rebuild failures.
*
* - In case of single failure, where rbio->failb == -1:
*
* Cache this rbio iff the above read reconstruction is
* excuted without problems.
*/
if (err == BLK_STS_OK && rbio->failb < 0)
cache_rbio_pages(rbio);
else
clear_bit(RBIO_CACHE_READY_BIT, &rbio->flags);