Re: [PATCH] perf: Fix race in perf_mmap_close function

[Jiri Olsa]

On Mon, Sep 14, 2020 at 09:48:43PM +0900, Namhyung Kim wrote:
> On Fri, Sep 11, 2020 at 4:49 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> > ugh, that's right.. how about change below
> 
> Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

thanks, I'll send full patch after we're done testing this

jirka

> 
> Thanks
> Namhyung
> 
> 
> >
> > jirka
> >
> >
> > ---
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 7ed5248f0445..8ab2400aef55 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -5868,11 +5868,11 @@ static void perf_pmu_output_stop(struct perf_event *event);
> >  static void perf_mmap_close(struct vm_area_struct *vma)
> >  {
> >         struct perf_event *event = vma->vm_file->private_data;
> > -
> >         struct perf_buffer *rb = ring_buffer_get(event);
> >         struct user_struct *mmap_user = rb->mmap_user;
> >         int mmap_locked = rb->mmap_locked;
> >         unsigned long size = perf_data_size(rb);
> > +       bool detach_rest = false;
> >
> >         if (event->pmu->event_unmapped)
> >                 event->pmu->event_unmapped(event, vma->vm_mm);
> > @@ -5903,7 +5903,8 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> >                 mutex_unlock(&event->mmap_mutex);
> >         }
> >
> > -       atomic_dec(&rb->mmap_count);
> > +       if (atomic_dec_and_test(&rb->mmap_count))
> > +               detach_rest = true;
> >
> >         if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
> >                 goto out_put;
> > @@ -5912,7 +5913,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> >         mutex_unlock(&event->mmap_mutex);
> >
> >         /* If there's still other mmap()s of this buffer, we're done. */
> > -       if (atomic_read(&rb->mmap_count))
> > +       if (!detach_rest)
> >                 goto out_put;
> >
> >         /*
> >
>