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authorPeter Zijlstra <peterz@infradead.org>2014-02-12 10:49:30 +0100
committerThomas Gleixner <tglx@linutronix.de>2014-02-21 21:43:18 +0100
commit3f1d2a318171bf61850d4e5a72031271e5aada76 (patch)
tree58b0fe5519ddeaac88983ff2ba9818f8695db726 /kernel/sched/sched.h
parent6e83125c6b151afa139c8852c099d6d92954fe3b (diff)
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 <juri.lelli@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Steven Rostedt <rostedt@goodmis.org> Reported-by: Kirill Tkhai <tkhai@yandex.ru> Reported-by: Dan Carpenter <dan.carpenter@oracle.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20140212094930.GB3545@laptop.programming.kicks-ass.net Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/sched/sched.h')
-rw-r--r--kernel/sched/sched.h5
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 92018f9821e8..d276147ba5e4 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1147,6 +1147,11 @@ struct sched_class {
#endif
};
+static inline void put_prev_task(struct rq *rq, struct task_struct *prev)
+{
+ prev->sched_class->put_prev_task(rq, prev);
+}
+
#define sched_class_highest (&stop_sched_class)
#define for_each_class(class) \
for (class = sched_class_highest; class; class = class->next)