From 81907478c4311a679849216abf723999184ab984 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Fri, 23 Jan 2015 08:25:38 +0000 Subject: [PATCH] sched/fair: Avoid using uninitialized variable in preferred_group_nid() At least some gcc versions - validly afaict - warn about potentially using max_group uninitialized: There's no way the compiler can prove that the body of the conditional where it and max_faults get set/ updated gets executed; in fact, without knowing all the details of other scheduler code, I can't prove this either. Generally the necessary change would appear to be to clear max_group prior to entering the inner loop, and break out of the outer loop when it ends up being all clear after the inner one. This, however, seems inefficient, and afaict the same effect can be achieved by exiting the outer loop when max_faults is still zero after the inner loop. [ mingo: changed the solution to zero initialization: uninitialized_var() needs to die, as it's an actively dangerous construct: if in the future a known-proven-good piece of code is changed to have a true, buggy uninitialized variable, the compiler warning is then supressed... The better long term solution is to clean up the code flow, so that even simple minded compilers (and humans!) are able to read it without getting a headache. ] Signed-off-by: Jan Beulich Signed-off-by: Peter Zijlstra (Intel) Cc: Rik van Riel Cc: Linus Torvalds Link: http://lkml.kernel.org/r/54C2139202000078000588F7@mail.emea.novell.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 40667cbf371b..fe331fc391f5 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1730,7 +1730,7 @@ static int preferred_group_nid(struct task_struct *p, int nid) nodes = node_online_map; for (dist = sched_max_numa_distance; dist > LOCAL_DISTANCE; dist--) { unsigned long max_faults = 0; - nodemask_t max_group; + nodemask_t max_group = NODE_MASK_NONE; int a, b; /* Are there nodes at this distance from each other? */ -- 2.30.2