While the stripe in-memory must be in-sync, the stripe on disk might not be
because if we computed a block rather than reading it from an in-sync disk,
the in-memory stripe can be different from the on-disk stripe.

If this bug were still in mainline I would probably want a bigger patch which
would leave this code but also set R5_LOCKED on all blocks that have been
computed.  But as it is a stablisation patch, the above is simple and more
clearly correct.

Thanks for you patience - I look forward to your success/failure report.

NeilBrown

diff -up /drivers/md/raid5.c
===========================================
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2466,8 +2466,6 @@
					locked++;
					set_bit(R5_Wantwrite, &sh->dev[i].flags);
				}
-			/* after a RECONSTRUCT_WRITE, the stripe MUST be in-sync */
-			set_bit(STRIPE_INSYNC, &sh->state);

			if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
				atomic_dec(&conf->preread_active_stripes);