Commit accaf6ea authored Nov 15, 2015 by Oleg Nesterov Committed by Ingo Molnar Nov 23, 2015

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: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Tejun 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: Ingo 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 @@ repeat:
		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;
		}
		}

Admin message