Commit b22366cd authored Feb 24, 2013 by Frederic Weisbecker

context_tracking: Restore preempted context state after preempt_schedule_irq()



From the context tracking POV, preempt_schedule_irq() behaves pretty much
like an exception: It can be called anytime and schedule another task.

But currently it doesn't restore the context tracking state of the preempted
code on preempt_schedule_irq() return.

As a result, if preempt_schedule_irq() is called in the tiny frame between
user_enter() and the actual return to userspace, we resume userspace with
the wrong context tracking state.

Fix this by using exception_enter/exit() which are a perfect fit for this
kind of issue.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Mats Liljegren <mats.liljegren@enea.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent 6c1e0256

kernel/sched/core.c

+5 −1

Original line number	Original line	Diff line number	Diff line
	@@ -3082,11 +3082,13 @@ EXPORT_SYMBOL(preempt_schedule);
	asmlinkage void __sched preempt_schedule_irq(void)		asmlinkage void __sched preempt_schedule_irq(void)
	{		{
	struct thread_info *ti = current_thread_info();		struct thread_info *ti = current_thread_info();
			enum ctx_state prev_state;

	/* Catch callers which need to be fixed */		/* Catch callers which need to be fixed */
	BUG_ON(ti->preempt_count \|\| !irqs_disabled());		BUG_ON(ti->preempt_count \|\| !irqs_disabled());

	user_exit();		prev_state = exception_enter();

	do {		do {
	add_preempt_count(PREEMPT_ACTIVE);		add_preempt_count(PREEMPT_ACTIVE);
	local_irq_enable();		local_irq_enable();
	@@ -3100,6 +3102,8 @@ asmlinkage void __sched preempt_schedule_irq(void)
	*/		*/
	barrier();		barrier();
	} while (need_resched());		} while (need_resched());

			exception_exit(prev_state);
	}		}

	#endif /* CONFIG_PREEMPT */		#endif /* CONFIG_PREEMPT */