Re: [PATCH] flow: Set EPOLLFD_ID_DEFAULT on newly allocated flows, not EPOLLFD_ID_INVALID

[Stefano Brivio <sbrivio@redhat.com>]

On Tue, 9 Dec 2025 10:36:01 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Mon, Dec 08, 2025 at 10:54:00PM +0100, Stefano Brivio wrote:
> > On Mon,  8 Dec 2025 22:28:22 +0100
> > Stefano Brivio <sbrivio@redhat.com> wrote:
> >   
> > > We're somehow hitting:
> > > 
> > >   ASSERTION FAILED in flow_epollfd (flow.c:362): f->epollid < ((1 << 8) - 1)
> > > 
> > > on an inbound spliced connection, with a single forwarded port, an
> > > HTTP server in a Podman container, and a GET request. Reproducer at
> > > https://bodhi.fedoraproject.org/updates/FEDORA-2025-93b4eb64c3#comment-4473411
> > > 
> > >   printf 'FROM registry.fedoraproject.org/fedora:latest\nRUN /usr/bin/dnf install -y httpd\nEXPOSE 80\nCMD ["-D", "FOREGROUND"]\nENTRYPOINT ["/usr/sbin/httpd"]\n' > Containerfile
> > >   podman build -t fedora-httpd $(pwd)
> > >   podman run -d -p 8080:80 localhost/fedora-httpd
> > > 
> > >   curl http://localhost:8080
> > > 
> > > I guess we don't set EPOLLFD_ID_DEFAULT early enough on inbound spliced
> > > sockets for some reason and we get a socket event while we still have
> > > EPOLLFD_ID_INVALID set.
> > > 
> > > As we're not really using epoll identifiers yet, set
> > > EPOLLFD_ID_DEFAULT right away on newly allocated flows, while we
> > > figure this out.
> > > 
> > > Link: https://bodhi.fedoraproject.org/updates/FEDORA-2025-93b4eb64c3#comment-4473411
> > > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> > > ---
> > > I just merged this, posting for awareness / review.  
> > 
> > Ah, never mind, this makes it worse somehow:
> > 
> > 5.6384: Flow 0 (TCP connection (spliced)): SPLICE_CONNECT
> > 5.6384: Flow 0 (TCP connection (spliced)): ERROR on epoll_ctl(): No such file or directory  
> 
> Does this imply you managed to reproduce locally?  You hadn't as of
> your comment a few after the one linked.  I also haven't managed to
> reproduce this.

Just simulate an error (that's not EINPROGRESS) on connect() in
tcp_splice_connect(). Patch coming.

-- 
Stefano