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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>
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1 changed files with 13 additions and 1 deletions
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@ -1201,9 +1201,21 @@ static int task_numa_migrate(struct task_struct *p)
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*/
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rcu_read_lock();
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sd = rcu_dereference(per_cpu(sd_numa, env.src_cpu));
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env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
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if (sd)
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env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
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rcu_read_unlock();
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/*
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* Cpusets can break the scheduler domain tree into smaller
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* balance domains, some of which do not cross NUMA boundaries.
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* Tasks that are "trapped" in such domains cannot be migrated
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* elsewhere, so there is no point in (re)trying.
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*/
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if (unlikely(!sd)) {
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p->numa_preferred_nid = cpu_to_node(task_cpu(p));
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return -EINVAL;
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}
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taskweight = task_weight(p, env.src_nid);
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groupweight = group_weight(p, env.src_nid);
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update_numa_stats(&env.src_stats, env.src_nid);
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