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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>
hifive-unleashed-5.1
Frederic Weisbecker 2013-02-24 12:59:30 +01:00
parent 6c1e0256fa
commit b22366cd54
1 changed files with 5 additions and 1 deletions
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6
kernel/sched/core.c
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@ -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 */