On Thu, Mar 12, 2026 at 02:17:16PM +0100, Eric Dumazet wrote: > On Thu, Mar 12, 2026 at 2:06 PM Simon Schippers > <[email protected]> wrote: > > > > This patch moves the check for available free space for a new entry into > > a separate function. As a result, __ptr_ring_produce() remains logically > > unchanged, while the new helper allows callers to determine in advance > > whether subsequent __ptr_ring_produce() calls will succeed. This > > information can, for example, be used to temporarily stop producing until > > __ptr_ring_peek() indicates that space is available again. > > > > Co-developed-by: Tim Gebauer <[email protected]> > > Signed-off-by: Tim Gebauer <[email protected]> > > Signed-off-by: Simon Schippers <[email protected]> > > --- > > include/linux/ptr_ring.h | 14 ++++++++++++-- > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h > > index 534531807d95..a5a3fa4916d3 100644 > > --- a/include/linux/ptr_ring.h > > +++ b/include/linux/ptr_ring.h > > @@ -96,6 +96,14 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r) > > return ret; > > } > > > > +static inline int __ptr_ring_produce_peek(struct ptr_ring *r) > > +{ > > + if (unlikely(!r->size) || r->queue[r->producer]) > > I think this should be > > if (unlikely(!r->size) || READ_ONCE(r->queue[r->producer])) > > And of course: > > @@ -194,7 +194,7 @@ static inline void *__ptr_ring_peek(struct ptr_ring *r) > static inline bool __ptr_ring_empty(struct ptr_ring *r) > { > if (likely(r->size)) > - return !r->queue[READ_ONCE(r->consumer_head)]; > + return !READ_ONCE(r->queue[READ_ONCE(r->consumer_head)]); > return true; > }
I don't understand why it's necessary. consumer_head etc are all lock protected. queue itself is not but we are only checking it for NULL - it is fine if compiler reads it in many chunks and not all at once. > @@ -256,7 +256,7 @@ static inline void __ptr_ring_zero_tail(struct > ptr_ring *r, int consumer_head) > * besides the first one until we write out all entries. > */ > while (likely(head > r->consumer_tail)) > - r->queue[--head] = NULL; > + WRITE_ONCE(r->queue[--head], NULL); > > r->consumer_tail = consumer_head; > } > > > Presumably we should fix this in net tree first. Maybe this one yes but I am not sure at all - KCSAN is happy. -- MST
