> From: Paolo Abeni <pabeni@xxxxxxxxxx> > Sent: Thursday, April 18, 2024 5:57 AM > On Thu, 2024-04-18 at 15:36 +0800, Heng Qi wrote: > > > > 在 2024/4/18 下午2:42, Jason Wang 写道: > > > On Wed, Apr 17, 2024 at 3:31 AM Daniel Jurgens <danielj@xxxxxxxxxx> > wrote: > > > > The command VQ will no longer be protected by the RTNL lock. Use a > > > > spinlock to protect the control buffer header and the VQ. > > > > > > > > Signed-off-by: Daniel Jurgens <danielj@xxxxxxxxxx> > > > > Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxx> > > > > --- > > > > drivers/net/virtio_net.c | 6 +++++- > > > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > > index 0ee192b45e1e..d02f83a919a7 100644 > > > > --- a/drivers/net/virtio_net.c > > > > +++ b/drivers/net/virtio_net.c > > > > @@ -282,6 +282,7 @@ struct virtnet_info { > > > > > > > > /* Has control virtqueue */ > > > > bool has_cvq; > > > > + spinlock_t cvq_lock; > > > Spinlock is instead of mutex which is problematic as there's no > > > guarantee on when the driver will get a reply. And it became even > > > more serious after 0d197a147164 ("virtio-net: add cond_resched() to > > > the command waiting loop"). > > > > > > Any reason we can't use mutex? > > > > Hi Jason, > > > > I made a patch set to enable ctrlq's irq on top of this patch set, > > which removes cond_resched(). > > > > But I need a little time to test, this is close to fast. So could the > > topic about cond_resched + spin lock or mutex lock be wait? > > The big problem is that until the cond_resched() is there, replacing the > mutex with a spinlock can/will lead to scheduling while atomic splats. We > can't intentionally introduce such scenario. When I created the series set_rx_mode wasn't moved to a work queue, and the cond_resched wasn't there. Mutex wasn't possible, then. If the CVQ is made to be event driven, then the lock can be released right after posting the work to the VQ. > > Side note: the compiler apparently does not like guard() construct, leading to > new warning, here and in later patches. I'm unsure if the code simplification > is worthy. I didn't see any warnings with GCC or clang. This is used other places in the kernel as well. gcc version 13.2.1 20230918 (Red Hat 13.2.1-3) (GCC) clang version 17.0.6 (Fedora 17.0.6-2.fc39) > > Cheers, > > Paolo