linux-kernel - Re: [syzbot] [netfs?] INFO: task hung in netfs_unbuffered_write

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Message-ID: <20250325130410.GA10828@redhat.com>
Date: Tue, 25 Mar 2025 14:04:10 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: K Prateek Nayak <kprateek.nayak@....com>,
	Eric Van Hensbergen <ericvh@...nel.org>,
	Latchesar Ionkov <lucho@...kov.net>,
	Dominique Martinet <asmadeus@...ewreck.org>,
	Christian Schoenebeck <linux_oss@...debyte.com>
Cc: Mateusz Guzik <mjguzik@...il.com>,
	syzbot <syzbot+62262fdc0e01d99573fc@...kaller.appspotmail.com>,
	brauner@...nel.org, dhowells@...hat.com, jack@...e.cz,
	jlayton@...nel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, netfs@...ts.linux.dev,
	swapnil.sapkal@....com, syzkaller-bugs@...glegroups.com,
	viro@...iv.linux.org.uk, v9fs@...ts.linux.dev
Subject: Re: [syzbot] [netfs?] INFO: task hung in netfs_unbuffered_write_iter

On 03/25, K Prateek Nayak wrote:
>
> I chased this down to p9_client_rpc() net/9p/client.c specifically:
>
>         err = c->trans_mod->request(c, req);
>         if (err < 0) {
>                 /* write won't happen */
>                 p9_req_put(c, req);
>                 if (err != -ERESTARTSYS && err != -EFAULT)
>                         c->status = Disconnected;
>                 goto recalc_sigpending;
>         }
>
> c->trans_mod->request() calls p9_fd_request() in net/9p/trans_fd.c
> which basically does a p9_fd_poll().

Again, I know nothing about 9p... but if p9_fd_request() returns
an err < 0, then it comes from p9_conn->err and p9_fd_request()
does nothing else.

> Previously, the above would fail with err as -EIO which would
> cause the client to "Disconnect" and the retry logic would make
> progress. Now however, the err returned is -ERESTARTSYS

OK... So p9_conn->err = -ERESTARTSYS was set by p9_conn_cancel()
called by p9_write_work() because pipe_write() returns ERESTARTSYS?

But I don't understand -EIO with the reverted commit aaec5a95d59615

Oleg.