From: Shaohua Li <shli@kernel.org>
Date: Tue, 15 Apr 2014 01:12:54 +0000 (+0800)
Subject: raid5: fix a race of stripe count check
X-Git-Tag: v4.9.8~6525^2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=c7a6d35e463caacab08ca0333bdec5b8bdce8bbb;p=platform%2Fkernel%2Flinux-rpi3.git

raid5: fix a race of stripe count check

I hit another BUG_ON with e240c1839d11152b0355442. In __get_priority_stripe(),
stripe count equals to 0 initially. Between atomic_inc and BUG_ON,
get_active_stripe() finds the stripe. So the stripe count isn't 1 any more.

V2: keeps the BUG_ON suggested by Neil.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>
---

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 25247a8..ad1b9be 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4370,8 +4370,7 @@ static struct stripe_head *__get_priority_stripe(struct r5conf *conf, int group)
 		sh->group = NULL;
 	}
 	list_del_init(&sh->lru);
-	atomic_inc(&sh->count);
-	BUG_ON(atomic_read(&sh->count) != 1);
+	BUG_ON(atomic_inc_return(&sh->count) != 1);
 	return sh;
 }