netdev - Re: [syzbot] [fs?] INFO: task hung in pipe

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Message-ID: <713503.1690644467@warthog.procyon.org.uk>
Date: Sat, 29 Jul 2023 16:27:47 +0100
From: David Howells <dhowells@...hat.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: dhowells@...hat.com,
    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: [syzbot] [fs?] INFO: task hung in pipe_release (4)

David Howells <dhowells@...hat.com> wrote:

> I've managed to reproduce it finally.  Instrumenting the pipe_lock/unlock
> functions, splice_to_socket() and pipe_release() seems to show that
> pipe_release() is being called whilst splice_to_socket() is still running.

That's actually a bit of a red herring.  pipe_release() is so-called because
it's called as the release file op for an end of the pipe.  It doesn't
automatically free the pipe_inode_info struct - there's refcounting on that.

So the problem is that udp_sendmsg() didn't return; pipe_release() hanging on
the pipe_lock() is merely a noisy symptom thereof.

David