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.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>
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