md/raid5: fix a recently broken BUG_ON().

commit 6d183de4077191d1201283a9035ce57a9b05254d
    md/raid5: fix newly-broken locking in get_active_stripe.

simplified a BUG_ON, but removed too much so now it sometimes fires
when it shouldn't.

When the STRIPE_EXPANDING flag is set, the stripe_head might be on a
special list while multiple stripe_heads are collected, or it might
not be on any list, even a 'free' list when the refcount is zero.  As
long as STRIPE_EXPANDING is set, it will be found and added back to a
list eventually.

So both of the BUG_ONs which test for the ->lru being empty or not
need to avoid the case where STRIPE_EXPANDING is set.

The patch which broke this was marked for -stable, so this patch needs
to be applied to any branch that received 6d183de4

Fixes: 6d183de4077191d1201283a9035ce57a9b05254d
Cc: stable@vger.kernel.org (any release to which above was applied)
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 9168173deaf3..cbb15716a5db 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -687,7 +687,8 @@ get_active_stripe(struct r5conf *conf, sector_t sector,
                         } else {
                                 if (!test_bit(STRIPE_HANDLE, &sh->state))
                                         atomic_inc(&conf->active_stripes);
-                                BUG_ON(list_empty(&sh->lru));
+                                BUG_ON(list_empty(&sh->lru) &&
+                                       !test_bit(STRIPE_EXPANDING, &sh->state));
                                 list_del_init(&sh->lru);
                                 if (sh->group) {
                                         sh->group->stripes_cnt--;