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sched: fix __pick_next_entity()
The thing is that __pick_next_entity() must never be called when first_fair(cfs_rq) == NULL. It wouldn't be a problem, should 'run_node' be the very first field of 'struct sched_entity' (and it's the second). The 'nr_running != 0' check is _not_ enough, due to the fact that 'current' is not within the tree. Generic paths are ok (e.g. schedule() as put_prev_task() is called previously)... I'm more worried about e.g. migration_call() -> CPU_DEAD_FROZEN -> migrate_dead_tasks()... if 'current' == rq->idle, no problems.. if it's one of the SCHED_NORMAL tasks (or imagine, some other use-cases in the future -- i.e. we should not make outer world dependent on internal details of sched_fair class) -- it may be "Houston, we've got a problem" case. it's +16 bytes to the ".text". Another variant is to make 'run_node' the first data member of 'struct sched_entity' but an additional check (se ! = NULL) is still needed in pick_next_entity(). Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
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@ -600,9 +600,12 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
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static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq)
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{
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struct sched_entity *se = __pick_next_entity(cfs_rq);
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struct sched_entity *se = NULL;
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set_next_entity(cfs_rq, se);
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if (first_fair(cfs_rq)) {
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se = __pick_next_entity(cfs_rq);
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set_next_entity(cfs_rq, se);
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}
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return se;
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}
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