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Commit accaf6ea authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
Browse files

stop_machine: Clean up the usage of the preemption counter in cpu_stopper_thread() 



1. Change this code to use preempt_count_inc/preempt_count_dec; this way
   it works even if CONFIG_PREEMPT_COUNT=n, and we avoid the unnecessary
   __preempt_schedule() check (stop_sched_class is not preemptible).

   And this makes clear that we only want to make preempt_count() != 0
   for __might_sleep() / schedule_debug().

2. Change WARN_ONCE() to use %pf to print the function name and remove
   kallsyms_lookup/ksym_buf.

3. Move "int ret" into the "if (work)" block, this looks more consistent.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Milos Vyletel <milos@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20151115193332.GA8281@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent dd2e3121

kernel/stop_machine.c

+5 −10
Original line number Diff line number Diff line
@@ -435,7 +435,6 @@ static void cpu_stopper_thread(unsigned int cpu) 
{

	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

	struct cpu_stop_work *work;

	int ret;



repeat:

	work = NULL;
@@ -451,23 +450,19 @@ static void cpu_stopper_thread(unsigned int cpu) 
		cpu_stop_fn_t fn = work->fn;

		void *arg = work->arg;

		struct cpu_stop_done *done = work->done;

		char ksym_buf[KSYM_NAME_LEN] __maybe_unused;

		int ret;



		/* cpu stop callbacks are not allowed to sleep */

		preempt_disable();

		/* cpu stop callbacks must not sleep, make in_atomic() == T */

		preempt_count_inc();

		ret = fn(arg);

		if (done) {

			if (ret)

				done->ret = ret;

			cpu_stop_signal_done(done);

		}

		/* restore preemption and check it's still balanced */

		preempt_enable();

		preempt_count_dec();

		WARN_ONCE(preempt_count(),

			  "cpu_stop: %s(%p) leaked preempt count\n",

			  kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,

					  ksym_buf), arg);



			  "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);

		goto repeat;

	}

}