On Fri, Jan 26, 2018 at 10:38:05AM +0800, Jason Wang wrote:
>
>
> On 2018年01月26日 07:36, Michael S. Tsirkin wrote:
> > Similar to bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can
> > overrun array bounds") a lockless use of __ptr_ring_full might
> > cause an out of bounds access.
> >
> > We can fix this, but it's easier to just disallow lockless
> > __ptr_ring_full for now.
>
> It looks to me that just fix this is better than disallow through doc (which
> is easily to be ignored ...).
>
> Thanks
lockless is tricky, and I'd rather not sprinkle READ/WRITE_ONCE where
they aren't necessary.
> >
> > Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
> > ---
> > include/linux/ptr_ring.h | 7 ++++---
> > 1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> > index 9a72d8f..f175846 100644
> > --- a/include/linux/ptr_ring.h
> > +++ b/include/linux/ptr_ring.h
> > @@ -45,9 +45,10 @@ struct ptr_ring {
> > };
> > /* Note: callers invoking this in a loop must use a compiler barrier,
> > - * for example cpu_relax(). If ring is ever resized, callers must hold
> > - * producer_lock - see e.g. ptr_ring_full. Otherwise, if callers don't
> > hold
> > - * producer_lock, the next call to __ptr_ring_produce may fail.
> > + * for example cpu_relax().
> > + *
> > + * NB: this is unlike __ptr_ring_empty in that callers must hold
> > producer_lock:
> > + * see e.g. ptr_ring_full.
> > */
> > static inline bool __ptr_ring_full(struct ptr_ring *r)
> > {
