md/raid5: Ensure a batch member is not handled prematurely.

If a stripe is a member of a batch, but not the head, it must
not be handled separately from the rest of the batch.

'clear_batch_ready()' handles this requirement to some
extent but not completely.  If a member is passed to handle_stripe()
a second time it returns '0' indicating the stripe can be handled,
which is wrong.
So add an extra test.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 42d0ea6c8597..e58736740bac 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4200,9 +4200,13 @@ static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s)
 
 static int clear_batch_ready(struct stripe_head *sh)
 {
+        /* Return '1' if this is a member of batch, or
+         * '0' if it is a lone stripe or a head which can now be
+         * handled.
+         */
         struct stripe_head *tmp;
         if (!test_and_clear_bit(STRIPE_BATCH_READY, &sh->state))
-                return 0;
+                return (sh->batch_head && sh->batch_head != sh);
         spin_lock(&sh->stripe_lock);
         if (!sh->batch_head) {
                 spin_unlock(&sh->stripe_lock);