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sched/numa: Fix NULL pointer dereference in task_numa_migrate() 

The cpusets code can split up the scheduler's domain tree into
smaller domains.  Some of those smaller domains may not cross
NUMA nodes at all, leading to a NULL pointer dereference on the
per-cpu sd_numa pointer.

Tasks cannot be migrated out of their domain, so the patch
also sets p->numa_preferred_nid to whereever they are, to
prevent the migration from being retried over and over again.

Reported-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Link: http://lkml.kernel.org/n/tip-oosqomw0Jput0Jkvoowhrqtu@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Rik van Riel 2013-11-11 19:29:25 -05:00 committed by Ingo Molnar
parent 106dd5afde
commit 46a73e8a1c
1 changed files with 13 additions and 1 deletions
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14
kernel/sched/fair.c
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@ -1201,9 +1201,21 @@ static int task_numa_migrate(struct task_struct *p)
*/ */
rcu_read_lock(); rcu_read_lock();
sd = rcu_dereference(per_cpu(sd_numa, env.src_cpu)); sd = rcu_dereference(per_cpu(sd_numa, env.src_cpu));
env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2; if (sd)
env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
rcu_read_unlock(); rcu_read_unlock();
/*
* Cpusets can break the scheduler domain tree into smaller
* balance domains, some of which do not cross NUMA boundaries.
* Tasks that are "trapped" in such domains cannot be migrated
* elsewhere, so there is no point in (re)trying.
*/
if (unlikely(!sd)) {
p->numa_preferred_nid = cpu_to_node(task_cpu(p));
return -EINVAL;
}
taskweight = task_weight(p, env.src_nid); taskweight = task_weight(p, env.src_nid);
groupweight = group_weight(p, env.src_nid); groupweight = group_weight(p, env.src_nid);
update_numa_stats(&env.src_stats, env.src_nid); update_numa_stats(&env.src_stats, env.src_nid);