From 08ec3df5109e0555da5b9deb4382fd29733c852c Mon Sep 17 00:00:00 2001 From: Dmitry Adamushko Date: Mon, 15 Oct 2007 17:00:13 +0200 Subject: [PATCH] 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 Signed-off-by: Ingo Molnar Reviewed-by: Thomas Gleixner --- kernel/sched_fair.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 1f14b56d0d0..fa78686ec22 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -600,9 +600,12 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se) static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq) { - struct sched_entity *se = __pick_next_entity(cfs_rq); + struct sched_entity *se = NULL; - set_next_entity(cfs_rq, se); + if (first_fair(cfs_rq)) { + se = __pick_next_entity(cfs_rq); + set_next_entity(cfs_rq, se); + } return se; } -- 2.41.0