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@xxxxxxxxxx>
---
fs/btrfs/raid56.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index 56ae5bd..4d56f24 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -1975,7 +1975,22 @@ static void __raid_recover_end_io(struct btrfs_raid_bio *rbio)
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);
--
2.9.4
--
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