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Subject[tip:sched/core] sched/deadline: Fix lock pinning warning during CPU hotplug
Commit-ID:  c0c8c9fa210c9a042060435f17e40ba4a76d6d6f
Gitweb: http://git.kernel.org/tip/c0c8c9fa210c9a042060435f17e40ba4a76d6d6f
Author: Wanpeng Li <wanpeng.li@hotmail.com>
AuthorDate: Thu, 4 Aug 2016 09:42:20 +0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 10 Aug 2016 14:02:55 +0200

sched/deadline: Fix lock pinning warning during CPU hotplug

The following warning can be triggered by hot-unplugging the CPU
on which an active SCHED_DEADLINE task is running on:

WARNING: CPU: 0 PID: 0 at kernel/locking/lockdep.c:3531 lock_release+0x690/0x6a0
releasing a pinned lock
Call Trace:
dump_stack+0x99/0xd0
__warn+0xd1/0xf0
? dl_task_timer+0x1a1/0x2b0
warn_slowpath_fmt+0x4f/0x60
? sched_clock+0x13/0x20
lock_release+0x690/0x6a0
? enqueue_pushable_dl_task+0x9b/0xa0
? enqueue_task_dl+0x1ca/0x480
_raw_spin_unlock+0x1f/0x40
dl_task_timer+0x1a1/0x2b0
? push_dl_task.part.31+0x190/0x190
WARNING: CPU: 0 PID: 0 at kernel/locking/lockdep.c:3649 lock_unpin_lock+0x181/0x1a0
unpinning an unpinned lock
Call Trace:
dump_stack+0x99/0xd0
__warn+0xd1/0xf0
warn_slowpath_fmt+0x4f/0x60
lock_unpin_lock+0x181/0x1a0
dl_task_timer+0x127/0x2b0
? push_dl_task.part.31+0x190/0x190

As per the comment before this code, its safe to drop the RQ lock
here, and since we (potentially) change rq, unpin and repin to avoid
the splat.

Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
[ Rewrote changelog. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luca Abeni <luca.abeni@unitn.it>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1470274940-17976-1-git-send-email-wanpeng.li@hotmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/deadline.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index fcb7f02..1ce8867 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -658,8 +658,11 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
*
* XXX figure out if select_task_rq_dl() deals with offline cpus.
*/
- if (unlikely(!rq->online))
+ if (unlikely(!rq->online)) {
+ lockdep_unpin_lock(&rq->lock, rf.cookie);
rq = dl_task_offline_migration(rq, p);
+ rf.cookie = lockdep_pin_lock(&rq->lock);
+ }

/*
* Queueing this task back might have overloaded rq, check if we need
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