Re: [PATCH 1/4] perf core: Introduce new ioctl options to pause and resume ring buffer

[Peter Zijlstra]

On Tue, Mar 29, 2016 at 02:54:23PM +0200, Peter Zijlstra wrote:
> +++ b/kernel/events/core.c
> @@ -4346,7 +4346,7 @@ static long _perf_ioctl(struct perf_even
>  
>               rcu_read_lock();
>               rb = rcu_dereference(event->rb);
> -             if (!event->rb) {
> +             if (!event->rb || !event->nr_pages) {
>                       rcu_read_unlock();
>                       return -EINVAL;
>               }

Clearly that should've been:

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4346,7 +4346,7 @@ static long _perf_ioctl(struct perf_even
 
                rcu_read_lock();
                rb = rcu_dereference(event->rb);
-               if (!event->rb || !event->nr_pages) {
+               if (!rb || !rb->nr_pages) {
                        rcu_read_unlock();
                        return -EINVAL;
                }