tree 073b8b6428f90c68e457fcbdfce5f12ea6ad42ac
parent 7d1311b93e58ed55f3a31cc8f94c4b8fe988a2b9
author NeilBrown <neilb@suse.de> 1407887325 +1000
committer NeilBrown <neilb@suse.de> 1408337381 +1000

md/raid5: avoid livelock caused by non-aligned writes.

If a stripe in a raid6 array received a write to each data block while
the array is degraded, and if any of these writes to a missing device
are not page-aligned, then a live-lock happens.

In this case the P and Q blocks need to be read so that the part of
the missing block which is *not* being updated by the write can be
constructed.  Due to a logic error, these blocks are not loaded, so
the update cannot proceed and the stripe is 'handled' repeatedly in an
infinite loop.

This bug is unlikely as most writes are page aligned.  However as it
can lead to a livelock it is suitable for -stable.  It was introduced
in 3.16.

Cc: stable@vger.kernel.org (v3.16)
Fixed: 67f455486d2ea20b2d94d6adf5b9b783d079e321
Signed-off-by: NeilBrown <neilb@suse.de>