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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>
This commit is contained in:
Oleg Nesterov 2015-11-15 20:33:32 +01:00 committed by Ingo Molnar
parent dd2e3121e3
commit accaf6ea3d
1 changed files with 5 additions and 10 deletions
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15
kernel/stop_machine.c
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@ -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;
}
}