Commit 1dc0fffc authored Sep 28, 2015 by Peter Zijlstra Committed by Ingo Molnar Oct 06, 2015

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.

This is most important on x86 which has a per cpu preempt_count that is
not saved/restored (after this series). So if you schedule with an
invalid (!2*PREEMPT_DISABLE_OFFSET) preempt_count the next task is
messed up too.

Enforcing this invariant limits the borkage to just the one task.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 3d8f74dd

kernel/exit.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -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)

kernel/sched/core.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -2968,8 +2968,10 @@ static inline void schedule_debug(struct task_struct *prev)
		BUG_ON(unlikely(task_stack_end_corrupted(prev)));
		#endif

		if (unlikely(in_atomic_preempt_off()))
		if (unlikely(in_atomic_preempt_off())) {
		__schedule_bug(prev);
		preempt_count_set(PREEMPT_DISABLED);
		}
		rcu_sleep_check();

		profile_hit(SCHED_PROFILING, __builtin_return_address(0));