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Commit 46a73e8a authored by Rik van Riel's avatar Rik van Riel Committed by Ingo Molnar
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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: default avatarPrarit Bhargava <prarit@redhat.com>
Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Link: http://lkml.kernel.org/n/tip-oosqomw0Jput0Jkvoowhrqtu@git.kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 106dd5af

kernel/sched/fair.c

+13 −1
Original line number Diff line number Diff line
@@ -1201,9 +1201,21 @@ static int task_numa_migrate(struct task_struct *p) 
	 */

	rcu_read_lock();

	sd = rcu_dereference(per_cpu(sd_numa, env.src_cpu));

	if (sd)

		env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;

	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);

	groupweight = group_weight(p, env.src_nid);

	update_numa_stats(&env.src_stats, env.src_nid);