| Message ID | 8a1740148995663939837bedb14f29716c7cf6f5.1526392746.git.pabeni@redhat.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
| Series | sched: refactor NOLOCK qdiscs | expand |
On Tue, May 15, 2018 at 04:24:37PM +0200, Paolo Abeni wrote: > After the previous patch, for NOLOCK qdiscs, q->seqlock is > always held when the dequeue() is invoked, we can drop > any additional locking to protect such operation. > > Signed-off-by: Paolo Abeni <pabeni@redhat.com> > --- > include/linux/skb_array.h | 5 +++++ > net/sched/sch_generic.c | 4 ++-- > 2 files changed, 7 insertions(+), 2 deletions(-) Is the seqlock taken during qdisc_change_tx_queue_len? We need to prevent that racing with dequeue. > diff --git a/include/linux/skb_array.h b/include/linux/skb_array.h > index a6b6e8bb3d7b..62d9b0a6329f 100644 > --- a/include/linux/skb_array.h > +++ b/include/linux/skb_array.h > @@ -97,6 +97,11 @@ static inline bool skb_array_empty_any(struct skb_array *a) > return ptr_ring_empty_any(&a->ring); > } > > +static inline struct sk_buff *__skb_array_consume(struct skb_array *a) > +{ > + return __ptr_ring_consume(&a->ring); > +} > + > static inline struct sk_buff *skb_array_consume(struct skb_array *a) > { > return ptr_ring_consume(&a->ring); > diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c > index a126f16bc30b..760ab1b09f8b 100644 > --- a/net/sched/sch_generic.c > +++ b/net/sched/sch_generic.c > @@ -656,7 +656,7 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc) > if (__skb_array_empty(q)) > continue; > > - skb = skb_array_consume_bh(q); > + skb = __skb_array_consume(q); > } > if (likely(skb)) { > qdisc_qstats_cpu_backlog_dec(qdisc, skb); > @@ -697,7 +697,7 @@ static void pfifo_fast_reset(struct Qdisc *qdisc) > if (!q->ring.queue) > continue; > > - while ((skb = skb_array_consume_bh(q)) != NULL) > + while ((skb = __skb_array_consume(q)) != NULL) > kfree_skb(skb); > } > > -- > 2.14.3
On Tue, 2018-05-15 at 23:17 +0300, Michael S. Tsirkin wrote: > On Tue, May 15, 2018 at 04:24:37PM +0200, Paolo Abeni wrote: > > After the previous patch, for NOLOCK qdiscs, q->seqlock is > > always held when the dequeue() is invoked, we can drop > > any additional locking to protect such operation. > > > > Signed-off-by: Paolo Abeni <pabeni@redhat.com> > > --- > > include/linux/skb_array.h | 5 +++++ > > net/sched/sch_generic.c | 4 ++-- > > 2 files changed, 7 insertions(+), 2 deletions(-) > > Is the seqlock taken during qdisc_change_tx_queue_len? > We need to prevent that racing with dequeue. Thanks for the head-up! I missed that code-path. I'll add the lock in qdisc_change_tx_queue_len() in v2. Thanks you, Paolo
On Wed, 2018-05-16 at 09:56 +0200, Paolo Abeni wrote: > On Tue, 2018-05-15 at 23:17 +0300, Michael S. Tsirkin wrote: > > On Tue, May 15, 2018 at 04:24:37PM +0200, Paolo Abeni wrote: > > > After the previous patch, for NOLOCK qdiscs, q->seqlock is > > > always held when the dequeue() is invoked, we can drop > > > any additional locking to protect such operation. > > > > > > Signed-off-by: Paolo Abeni <pabeni@redhat.com> > > > --- > > > include/linux/skb_array.h | 5 +++++ > > > net/sched/sch_generic.c | 4 ++-- > > > 2 files changed, 7 insertions(+), 2 deletions(-) > > > > Is the seqlock taken during qdisc_change_tx_queue_len? > > We need to prevent that racing with dequeue. > > Thanks for the head-up! I missed that code-path. > > I'll add the lock in qdisc_change_tx_queue_len() in v2. Actually the lock is not needed in qdisc_change_tx_queue_len(): the device is deactivated before calling ops->change_tx_queue_len, so the latter can't race with ops->dequeue(). I think the current patch is safe. Cheers, Paolo
On Wed, May 16, 2018 at 09:56:16AM +0200, Paolo Abeni wrote: > On Tue, 2018-05-15 at 23:17 +0300, Michael S. Tsirkin wrote: > > On Tue, May 15, 2018 at 04:24:37PM +0200, Paolo Abeni wrote: > > > After the previous patch, for NOLOCK qdiscs, q->seqlock is > > > always held when the dequeue() is invoked, we can drop > > > any additional locking to protect such operation. > > > > > > Signed-off-by: Paolo Abeni <pabeni@redhat.com> > > > --- > > > include/linux/skb_array.h | 5 +++++ > > > net/sched/sch_generic.c | 4 ++-- > > > 2 files changed, 7 insertions(+), 2 deletions(-) > > > > Is the seqlock taken during qdisc_change_tx_queue_len? > > We need to prevent that racing with dequeue. > > Thanks for the head-up! I missed that code-path. > > I'll add the lock in qdisc_change_tx_queue_len() in v2. > > Thanks you, > > Paolo When you do, make sure locks nest consistently.
diff --git a/include/linux/skb_array.h b/include/linux/skb_array.h index a6b6e8bb3d7b..62d9b0a6329f 100644 --- a/include/linux/skb_array.h +++ b/include/linux/skb_array.h @@ -97,6 +97,11 @@ static inline bool skb_array_empty_any(struct skb_array *a) return ptr_ring_empty_any(&a->ring); } +static inline struct sk_buff *__skb_array_consume(struct skb_array *a) +{ + return __ptr_ring_consume(&a->ring); +} + static inline struct sk_buff *skb_array_consume(struct skb_array *a) { return ptr_ring_consume(&a->ring); diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index a126f16bc30b..760ab1b09f8b 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -656,7 +656,7 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc) if (__skb_array_empty(q)) continue; - skb = skb_array_consume_bh(q); + skb = __skb_array_consume(q); } if (likely(skb)) { qdisc_qstats_cpu_backlog_dec(qdisc, skb); @@ -697,7 +697,7 @@ static void pfifo_fast_reset(struct Qdisc *qdisc) if (!q->ring.queue) continue; - while ((skb = skb_array_consume_bh(q)) != NULL) + while ((skb = __skb_array_consume(q)) != NULL) kfree_skb(skb); }
After the previous patch, for NOLOCK qdiscs, q->seqlock is always held when the dequeue() is invoked, we can drop any additional locking to protect such operation. Signed-off-by: Paolo Abeni <pabeni@redhat.com> --- include/linux/skb_array.h | 5 +++++ net/sched/sch_generic.c | 4 ++-- 2 files changed, 7 insertions(+), 2 deletions(-)