linux-kernel - Re: [PATCH net-next v8 01/14] vsock: a per-net vsock NS mode state

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Message-ID: <aQ1Gyp87UYnr/VAO@devvm11784.nha0.facebook.com>
Date: Thu, 6 Nov 2025 17:09:30 -0800
From: Bobby Eshleman <bobbyeshleman@...il.com>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: Shuah Khan <shuah@...nel.org>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Bryan Tan <bryan-bt.tan@...adcom.com>,
	Vishnu Dasa <vishnu.dasa@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	virtualization@...ts.linux.dev, netdev@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, linux-hyperv@...r.kernel.org,
	berrange@...hat.com, Bobby Eshleman <bobbyeshleman@...a.com>
Subject: Re: [PATCH net-next v8 01/14] vsock: a per-net vsock NS mode state

On Thu, Nov 06, 2025 at 05:16:29PM +0100, Stefano Garzarella wrote:
> On Thu, Oct 23, 2025 at 11:27:40AM -0700, Bobby Eshleman wrote:
> > From: Bobby Eshleman <bobbyeshleman@...a.com>

[...]

> > @@ -65,6 +66,7 @@ struct vsock_sock {
> > 	u32 peer_shutdown;
> > 	bool sent_request;
> > 	bool ignore_connecting_rst;
> > +	enum vsock_net_mode net_mode;
> > 
> > 	/* Protected by lock_sock(sk) */
> > 	u64 buffer_size;
> > @@ -256,4 +258,58 @@ static inline bool vsock_msgzerocopy_allow(const struct vsock_transport *t)
> > {
> > 	return t->msgzerocopy_allow && t->msgzerocopy_allow();
> > }
> > +
> > +static inline enum vsock_net_mode vsock_net_mode(struct net *net)
> > +{
> > +	enum vsock_net_mode ret;
> > +
> > +	spin_lock_bh(&net->vsock.lock);
> > +	ret = net->vsock.mode;
> 
> Do we really need a spin_lock just to set/get a variable?
> What about WRITE_ONCE/READ_ONCE and/or atomic ?
> 
> Not a strong opinion, just to check if we can do something like this:
> 
> static inline enum vsock_net_mode vsock_net_mode(struct net *net)
> {
>     return READ_ONCE(net->vsock.mode);
> }
> 
> static inline bool vsock_net_write_mode(struct net *net, u8 mode)
> {
>     // Or using test_and_set_bit() if you prefer
>     if (xchg(&net->vsock.mode_locked, true))
>         return false;
> 
>     WRITE_ONCE(net->vsock.mode, mode);
>     return true;
> }
> 

I think that works and seems worth it to avoid the lock on the read
side. I'll move this over for the next rev.

[...]

Best,
Bobby