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>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 9168173deaf307b5524448284a6f59ef81558e33..cbb15716a5db31cf39a08b6a8a9df45d0bc9e0dc 100644 (file)
--- 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--;