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

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Message-ID: <20250328144928.GC29527@redhat.com>
Date: Fri, 28 Mar 2025 15:49:28 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: syzbot <syzbot+62262fdc0e01d99573fc@...kaller.appspotmail.com>
Cc: asmadeus@...ewreck.org, brauner@...nel.org, dhowells@...hat.com,
	ericvh@...nel.org, jack@...e.cz, jlayton@...nel.org,
	kprateek.nayak@....com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux_oss@...debyte.com,
	lucho@...kov.net, mjguzik@...il.com, netfs@...ts.linux.dev,
	swapnil.sapkal@....com, syzkaller-bugs@...glegroups.com,
	v9fs@...ts.linux.dev, viro@...iv.linux.org.uk
Subject: Re: [syzbot] [netfs?] INFO: task hung in netfs_unbuffered_write_iter

On 03/28, syzbot wrote:
>
> Hello,
>
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> unregister_netdevice: waiting for DEV to become free
>
> unregister_netdevice: waiting for batadv0 to become free. Usage count = 3

Looks "obviously unrelated", but I'm not sure about anything anymore.

In any case I leave this to 9p maintainers.

Okay, just out of curiosity:

#syz test: upstream aaec5a95d59615523db03dd53c2052f0a87beea7


diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index 56e62978e502..aa9cd248a243 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -669,7 +669,6 @@ static void p9_poll_mux(struct p9_conn *m)
 
 static int p9_fd_request(struct p9_client *client, struct p9_req_t *req)
 {
-	__poll_t n;
 	struct p9_trans_fd *ts = client->trans;
 	struct p9_conn *m = &ts->conn;
 
@@ -687,13 +686,7 @@ static int p9_fd_request(struct p9_client *client, struct p9_req_t *req)
 	list_add_tail(&req->req_list, &m->unsent_req_list);
 	spin_unlock(&m->req_lock);
 
-	if (test_and_clear_bit(Wpending, &m->wsched))
-		n = EPOLLOUT;
-	else
-		n = p9_fd_poll(m->client, NULL, NULL);
-
-	if (n & EPOLLOUT && !test_and_set_bit(Wworksched, &m->wsched))
-		schedule_work(&m->wq);
+	p9_poll_mux(m);
 
 	return 0;
 }