From 3f1d2a318171bf61850d4e5a72031271e5aada76 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 12 Feb 2014 10:49:30 +0100 Subject: sched: Fix hotplug task migration Dan Carpenter reported: > kernel/sched/rt.c:1347 pick_next_task_rt() warn: variable dereferenced before check 'prev' (see line 1338) > kernel/sched/deadline.c:1011 pick_next_task_dl() warn: variable dereferenced before check 'prev' (see line 1005) Kirill also spotted that migrate_tasks() will have an instant NULL deref because pick_next_task() will immediately deref prev. Instead of fixing all the corner cases because migrate_tasks() can pass in a NULL prev task in the unlikely case of hot-un-plug, provide a fake task such that we can remove all the NULL checks from the far more common paths. A further problem; not previously spotted; is that because we pushed pre_schedule() and idle_balance() into pick_next_task() we now need to avoid those getting called and pulling more tasks on our dying CPU. We avoid pull_{dl,rt}_task() by setting fake_task.prio to MAX_PRIO+1. We also note that since we call pick_next_task() exactly the amount of times we have runnable tasks present, we should never land in idle_balance(). Fixes: 38033c37faab ("sched: Push down pre_schedule() and idle_balance()") Cc: Juri Lelli Cc: Ingo Molnar Cc: Steven Rostedt Reported-by: Kirill Tkhai Reported-by: Dan Carpenter Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20140212094930.GB3545@laptop.programming.kicks-ass.net Signed-off-by: Thomas Gleixner --- kernel/sched/stop_task.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'kernel/sched/stop_task.c') diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c index a4147c9d2017..d6ce65dde541 100644 --- a/kernel/sched/stop_task.c +++ b/kernel/sched/stop_task.c @@ -31,8 +31,7 @@ pick_next_task_stop(struct rq *rq, struct task_struct *prev) if (!stop || !stop->on_rq) return NULL; - if (prev) - prev->sched_class->put_prev_task(rq, prev); + put_prev_task(rq, prev); stop->se.exec_start = rq_clock_task(rq); -- cgit v1.2.3