Subject: Re: [PATCH net-next 2/2] pfifo_fast: drop unneeded additional lock on dequeue

From: Paolo Abeni <[email-masked]>
Date: Wed, 16 May 2018 09:56:16 +0200

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 <[email-masked]>
> > ---
> >  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