netdev - Re: Endless loop in udp with MSG_SPLICE_READ - Re: [syzbot] [fs?] INFO: task hung in pipe

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Date: Tue, 01 Aug 2023 15:02:57 +0100
From: David Howells <dhowells@...hat.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: dhowells@...hat.com, Jakub Kicinski <kuba@...nel.org>,
    syzbot <syzbot+f527b971b4bdc8e79f9e@...kaller.appspotmail.com>,
    bpf@...r.kernel.org, brauner@...nel.org, davem@...emloft.net,
    dsahern@...nel.org, edumazet@...gle.com,
    linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
    netdev@...r.kernel.org, pabeni@...hat.com,
    syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: Endless loop in udp with MSG_SPLICE_READ - Re: [syzbot] [fs?] INFO: task hung in pipe_release (4)

Willem de Bruijn <willemdebruijn.kernel@...il.com> wrote:

> What causes the infinite loop: does skb_splice_from_iter return 0 and
> therefore the loop neither decrements copy, nor breaks out with error?

Yeah.  skb_splice_from_iter() starts returning 0 because the iterator is
empty, but it's still being asked to copy data.  Possibly it should break out
of the loop (or give an error) in such a case.

David