[PATCH] sched/core: Fix rq lock pinning warning after call balance callbacks

[PATCH] sched/core: Fix rq lock pinning warning after call balance callbacks

[Wanpeng Li]

From: Wanpeng Li <wanpeng.li@hotmail.com>

This can be reproduced by running rt-migrate-test:

 WARNING: CPU: 2 PID: 2195 at kernel/locking/lockdep.c:3670 lock_unpin_lock+0x172/0x180
 unpinning an unpinned lock
 CPU: 2 PID: 2195 Comm: rt-migrate-test Tainted: G        W       4.11.0-rc2+ #1
 Call Trace:
  dump_stack+0x85/0xc2
  __warn+0xcb/0xf0
  warn_slowpath_fmt+0x5f/0x80
  lock_unpin_lock+0x172/0x180
  __balance_callback+0x75/0x90
  __schedule+0x83f/0xc00
  ? futex_wait_setup+0x82/0x130
  schedule+0x3d/0x90
  futex_wait_queue_me+0xd4/0x170
  futex_wait+0x119/0x260
  ? __lock_acquire+0x4c8/0x1900
  ? stop_one_cpu+0x94/0xc0
  do_futex+0x2fe/0xc10
  ? sched_setaffinity+0x1c1/0x290
  SyS_futex+0x81/0x190
  ? rcu_read_lock_sched_held+0x72/0x80
  do_syscall_64+0x73/0x1f0
  entry_SYSCALL64_slow_path+0x25/0x25

We utilize balance callbacks to delay the load-balancing operations 
{rt,dl}*{push,pull} until we've done all the important work. The 
push/pull operations can unlock/lock the current rq for safety acquires 
the src's and dest's rq->locks in a fair way. It's safe to drop the 
rq lock here, unpin and repin to avoid the splat.
	
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 kernel/sched/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c762f62..cd901f6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2787,7 +2787,9 @@ static void __balance_callback(struct rq *rq)
 		head->next = NULL;
 		head = next;
 
+		rq_unpin_lock(rq, &rf);
 		func(rq);
+		rq_repin_lock(rq, &rf);
 	}
 	rq_unlock_irqrestore(rq, &rf);
 }
-- 
2.7.4

[tip:sched/core] sched/core: Fix rq lock pinning warning after call balance callbacks

[tip-bot for Wanpeng Li]

Commit-ID:  d7921a5ddab8d30e06e321f37eec629f23797486
Gitweb:     http://git.kernel.org/tip/d7921a5ddab8d30e06e321f37eec629f23797486
Author:     Wanpeng Li <wanpeng.li@hotmail.com>
AuthorDate: Thu, 16 Mar 2017 19:45:19 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 23 Mar 2017 07:44:51 +0100

sched/core: Fix rq lock pinning warning after call balance callbacks

This can be reproduced by running rt-migrate-test:

 WARNING: CPU: 2 PID: 2195 at kernel/locking/lockdep.c:3670 lock_unpin_lock()
 unpinning an unpinned lock
 ...
 Call Trace:
  dump_stack()
  __warn()
  warn_slowpath_fmt()
  lock_unpin_lock()
  __balance_callback()
  __schedule()
  schedule()
  futex_wait_queue_me()
  futex_wait()
  do_futex()
  SyS_futex()
  do_syscall_64()
  entry_SYSCALL64_slow_path()

Revert the rq_lock_irqsave() usage here, the whole point of the
balance_callback() was to allow dropping rq->lock.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 8a8c69c32778 ("sched/core: Add rq->lock wrappers")
Link: http://lkml.kernel.org/r/1489718719-3951-1-git-send-email-wanpeng.li@hotmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c762f62..ab9f6ac 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2776,9 +2776,9 @@ static void __balance_callback(struct rq *rq)
 {
 	struct callback_head *head, *next;
 	void (*func)(struct rq *rq);
-	struct rq_flags rf;
+	unsigned long flags;
 
-	rq_lock_irqsave(rq, &rf);
+	raw_spin_lock_irqsave(&rq->lock, flags);
 	head = rq->balance_callback;
 	rq->balance_callback = NULL;
 	while (head) {
@@ -2789,7 +2789,7 @@ static void __balance_callback(struct rq *rq)
 
 		func(rq);
 	}
-	rq_unlock_irqrestore(rq, &rf);
+	raw_spin_unlock_irqrestore(&rq->lock, flags);
 }
 
 static inline void balance_callback(struct rq *rq)