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| author | Peter Zijlstra <peterz@infradead.org> | 2014-02-12 13:49:30 +0400 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2014-02-22 00:43:18 +0400 |
| commit | 3f1d2a318171bf61850d4e5a72031271e5aada76 (patch) | |
| tree | 58b0fe5519ddeaac88983ff2ba9818f8695db726 /kernel/sched/idle_task.c | |
| parent | 6e83125c6b151afa139c8852c099d6d92954fe3b (diff) | |
| download | linux-3f1d2a318171bf61850d4e5a72031271e5aada76.tar.xz | |
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/idle_task.c')
| -rw-r--r-- | kernel/sched/idle_task.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/kernel/sched/idle_task.c b/kernel/sched/idle_task.c index f7d03af79a5b..53ff9e7c76d2 100644 --- a/kernel/sched/idle_task.c +++ b/kernel/sched/idle_task.c @@ -26,8 +26,7 @@ static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int fl static struct task_struct * pick_next_task_idle(struct rq *rq, struct task_struct *prev) { - if (prev) - prev->sched_class->put_prev_task(rq, prev); + put_prev_task(rq, prev); schedstat_inc(rq, sched_goidle); #ifdef CONFIG_SMP |