Commit 44ac474d authored Jan 12, 2018 by Liu Bo Committed by David Sterba Jan 22, 2018

Btrfs: do not cache rbio pages if using raid6 recover



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>

parent 0198e5b7

fs/btrfs/raid56.c

+16 −1

Original line number	Diff line number	Diff line
		@@ -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);

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