[PATCH 8/8] stop_machine: cleanup the usage of preemption counter in cpu_stopper_thread()

Oleg Nesterov
2015-11-15T18:37:36Z

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>
---
kernel/stop_machine.c | 15 +++++----------
1 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 7ff7ace..6110119 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -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;
}
}
--
1.5.5.1