linux-kernel - [PATCH] mm/memcontrol: avoid a spurious gcc warning

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Date:	Mon, 25 Jan 2016 16:45:50 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Arnd Bergmann <arnd@...db.de>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH] mm/memcontrol: avoid a spurious gcc warning

When CONFIG_DEBUG_VM is set, the various VM_BUG_ON() confuse gcc to
the point where it cannot remember that 'memcg' is known to be initialized:

mm/memcontrol.c: In function 'mem_cgroup_can_attach':
mm/memcontrol.c:4791:9: warning: 'memcg' may be used uninitialized in this function [-Wmaybe-uninitialized]

On ARM gcc-5.1, the above happens when any two or more of the VM_BUG_ON()
are active, but not when I remove most or all of them. This is clearly
random behavior and the only way I've found to shut up the warning is
to add an explicit initialization.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 mm/memcontrol.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d06cae2de783..9340eb981653 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4762,6 +4762,7 @@ static int mem_cgroup_can_attach(struct cgroup_taskset *tset)
 	 * multiple.
 	 */
 	p = NULL;
+	memcg = NULL;
 	cgroup_taskset_for_each_leader(leader, css, tset) {
 		WARN_ON_ONCE(p);
 		p = leader;
-- 
2.7.0