Commit 1417f897 authored by NeilBrown's avatar NeilBrown Committed by Ben Hutchings

md/raid6: avoid data corruption during recovery of double-degraded RAID6

commit 9c4bdf69 upstream.

During recovery of a double-degraded RAID6 it is possible for
some blocks not to be recovered properly, leading to corruption.

If a write happens to one block in a stripe that would be written to a
missing device, and at the same time that stripe is recovering data
to the other missing device, then that recovered data may not be written.

This patch skips, in the double-degraded case, an optimisation that is
only safe for single-degraded arrays.

Bug was introduced in 2.6.32 and fix is suitable for any kernel since
then.  In an older kernel with separate handle_stripe5() and
handle_stripe6() functions the patch must change handle_stripe6().

Fixes: 6c0069c0
Cc: Yuri Tikhonov <yur@emcraft.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Reported-by: default avatar"Manibalan P" <pmanibalan@amiindia.co.in>
Tested-by: default avatar"Manibalan P" <pmanibalan@amiindia.co.in>
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1090423Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Acked-by: default avatarDan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
parent 9c50d4fd
......@@ -3240,6 +3240,8 @@ static void handle_stripe(struct stripe_head *sh)
set_bit(R5_Wantwrite, &dev->flags);
if (prexor)
continue;
if (s.failed > 1)
continue;
if (!test_bit(R5_Insync, &dev->flags) ||
((i == sh->pd_idx || i == sh->qd_idx) &&
s.failed == 0))
......
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