[PATCH 4.9 11/39] Revert "Btrfs: fix scrub to repair raid6 corruption"

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sasha Levin <Alexander.Levin@microsoft.com>

This reverts commit 186a6519dc94964a4c5c68fca482f20f71551f26.

This commit used an incorrect log message.

Reported-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/btrfs/raid56.c  |   18 ++++--------------
 fs/btrfs/volumes.c |    9 +--------
 2 files changed, 5 insertions(+), 22 deletions(-)

--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -2161,21 +2161,11 @@ int raid56_parity_recover(struct btrfs_r
 	}
 
 	/*
-	 * Loop retry:
-	 * for 'mirror == 2', reconstruct from all other stripes.
-	 * for 'mirror_num > 2', select a stripe to fail on every retry.
+	 * reconstruct from the q stripe if they are
+	 * asking for mirror 3
 	 */
-	if (mirror_num > 2) {
-		/*
-		 * 'mirror == 3' is to fail the p stripe and
-		 * reconstruct from the q stripe.  'mirror > 3' is to
-		 * fail a data stripe and reconstruct from p+q stripe.
-		 */
-		rbio->failb = rbio->real_stripes - (mirror_num - 1);
-		ASSERT(rbio->failb > 0);
-		if (rbio->failb <= rbio->faila)
-			rbio->failb--;
-	}
+	if (mirror_num == 3)
+		rbio->failb = rbio->real_stripes - 2;
 
 	ret = lock_stripe_add(rbio);
 
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5186,14 +5186,7 @@ int btrfs_num_copies(struct btrfs_fs_inf
 	else if (map->type & BTRFS_BLOCK_GROUP_RAID5)
 		ret = 2;
 	else if (map->type & BTRFS_BLOCK_GROUP_RAID6)
-		/*
-		 * There could be two corrupted data stripes, we need
-		 * to loop retry in order to rebuild the correct data.
-		 *
-		 * Fail a stripe at a time on every retry except the
-		 * stripe under reconstruction.
-		 */
-		ret = map->num_stripes;
+		ret = 3;
 	else
 		ret = 1;
 	free_extent_map(em);