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

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

		user_exit();
		prev_state = exception_enter();

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

		exception_exit(prev_state);
		}

		#endif /* CONFIG_PREEMPT */

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