Re: [PATCH net v5] vsock/bpf: release sock lock while waiting for data in recvmsg

[Stefano Garzarella]

On Thu, Nov 12, 2026 at 07:47:11PM +0000, jrmmhm.kernel@xxxxxxxxx wrote:
> On Thu, Nov 12, 2026 at 06:23:00PM +0100, Stefano Garzarella wrote:
> > On Mon, Nov 09, 2026 at 09:08:29PM +0100, Jerome Mohm via B4 Relay
> > wrote:
> > > The loop
> > > and the zero-length check belong to the fix (without them the reader
> > > returns early or spins with the lock held), so this is one patch;
> >
> > I don't understand why that fix can't be in a fist patch of the
> > series...
> >
> > > +    if (unlikely(!len || (flags & (MSG_OOB | MSG_ERRQUEUE))))
> > > +        return __vsock_recvmsg(sk, msg, len, flags);
> >
> > ... I mean, why this change ^^^ can't be in patch 1/2?
> >
> > BTW I'm not asking to split it (at least for now).
>
> It can: the loop is needed for the deadlock fix, since without it the
> reader returns -EAGAIN early when it wakes without data, but the early
> return isn't. A zero-length read with data in the psock queue already
> spins with the lock held on net, and as far as I can tell from the code
> the early return alone fixes that, plus the MSG_OOB and MSG_ERRQUEUE
> cases. In v4 those reads were patch 2/2. They went into one patch only
> because Alexei's diff replaced both, and my v5 sentence justified that
> badly. You said you're not asking for a split, but since the early
> return isn't needed for the deadlock, it would fit as its own patch:
> should v6 have it as 1/2 and the lock change as 2/2, or stay one patch?

Yeah, I'd prefer 2 patches with this change as first patch.

> > I saw some comments from sashiko, can you reply to them?
>
> I'll wait for your answer before sending v6, and I'm replying to the
> Sashiko comments separately.

Great, thanks for that!

Stefano