[tip:sched/core] sched/core: Robustify preemption leak checks

[tip-bot for Peter Zijlstra <tipbot@zytor.com>]

Commit-ID:  185b42420b0948dfc00af6cc5d93aa00b7fef581
Gitweb:     http://git.kernel.org/tip/185b42420b0948dfc00af6cc5d93aa00b7fef581
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 29 Sep 2015 11:28:28 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 29 Sep 2015 12:27:40 +0200

sched/core: Robustify preemption leak checks

When we warn about a preempt_count leak; reset the preempt_count
to the known good value such that the problem does not ripple
forward.

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>
Cc: fweisbec@gmail.com
Cc: linux-kernel@vger.kernel.org
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Cc: umgwanakikbuti@gmail.com
Link: http://lkml.kernel.org/r/20150929093519.930244771@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/exit.c       | 4 +++-
 kernel/sched/core.c | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index ea95ee1..443677c 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -706,10 +706,12 @@ void do_exit(long code)
 	smp_mb();
 	raw_spin_unlock_wait(&tsk->pi_lock);
 
-	if (unlikely(in_atomic()))
+	if (unlikely(in_atomic())) {
 		pr_info("note: %s[%d] exited with preempt_count %d\n",
 			current->comm, task_pid_nr(current),
 			preempt_count());
+		preempt_count_set(PREEMPT_ENABLED);
+	}
 
 	/* sync mm's RSS info before statistics gathering */
 	if (tsk->mm)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ecd585c..d1dec5d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2953,8 +2953,10 @@ static inline void schedule_debug(struct task_struct *prev)
 	 * schedule() atomically, we ignore that path. Otherwise whine
 	 * if we are scheduling when we should not.
 	 */
-	if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD))
+	if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD)) {
 		__schedule_bug(prev);
+		preempt_count_set(PREEMPT_DISABLED);
+	}
 	rcu_sleep_check();
 
 	profile_hit(SCHED_PROFILING, __builtin_return_address(0));