md: Fix data corruption when a degraded raid5 array is reshaped.

This patch fixes a fairly serious bug in md/raid5 in 2.6.23 and 24-rc. It would be great if it cold get into 23.13 and 24.final. Thanks.
NeilBrown

### Comments for Changeset

We currently do not wait for the block from the missing device to be computed from parity before copying data to the new stripe layout.

The change in the raid6 code is not techincally needed as we don't delay data block recovery in the same way for raid6 yet. But making the change now is safer long-term.

This bug exists in 2.6.23 and 2.6.24-rc

### Diffstat output

 ./drivers/md/raid5.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff .prev/drivers/md/raid5.c ./drivers/md/raid5.c
@@ -2865,7 +2865,7 @@ static void handle_stripe5(struct stripe
 		md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
 	}
 
-	if (s.expanding && s.locked == 0)
+	if (s.expanding && s.locked == 0 && s.req_compute == 0)
 		handle_stripe_expansion(conf, sh, NULL);
 
 	if (sh->ops.count)

@@ -3067,7 +3067,7 @@ static void handle_stripe6(struct stripe
 		md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
 	}
 
-	if (s.expanding && s.locked == 0)
+	if (s.expanding && s.locked == 0 && s.req_compute == 0)
 		handle_stripe_expansion(conf, sh, &r6s);
 
 	spin_unlock(&sh->lock);

On closer look the safer test is:

	!test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending).

The 'req_compute' field only indicates that a 'compute_block' operation was requested during this pass through handle_stripe so that we can issue a linked chain of asynchronous operations.

---

From: Neil Brown <[email protected]>

md: Fix data corruption when a degraded raid5 array is reshaped.

We currently do not wait for the block from the missing device to be computed from parity before copying data to the new stripe layout.

The change in the raid6 code is not techincally needed as we don't delay data block recovery in the same way for raid6 yet. But making the change now is safer long-term.

This bug exists in 2.6.23 and 2.6.24-rc

---

 drivers/md/raid5.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

index a5aad8c..e8c8157 100644
@@ -2865,7 +2865,8 @@ static void handle_stripe5(struct stripe_head *sh)
 		md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
 	}
 
-	if (s.expanding && s.locked == 0)
+	if (s.expanding && s.locked == 0 &&
+	    !test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending))
 		handle_stripe_expansion(conf, sh, NULL);
 
 	if (sh->ops.count)

@@ -3067,7 +3068,8 @@ static void handle_stripe6(struct stripe_head *sh, struct page *tmp_page)
 		md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
 	}
 
-	if (s.expanding && s.locked == 0)
+	if (s.expanding && s.locked == 0 &&
+	    !test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending))
 		handle_stripe_expansion(conf, sh, &r6s);
 
 	spin_unlock(&sh->lock);

Technically that should probably be
From: Dan Williams <[email protected]>

now, and then I add

because I completely agree with your improvement.

We should keep an eye out for then Andrew commits this and make sure the right patch goes in...

Thanks,
NeilBrown