linux-kernel - Re: [syzbot] [fs?] [mm?] INFO: task hung in v9fs_file

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Message-ID: <20250818130419.GD18626@redhat.com>
Date: Mon, 18 Aug 2025 15:04:20 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: syzbot <syzbot+d1b5dace43896bc386c3@...kaller.appspotmail.com>,
	David Howells <dhowells@...hat.com>,
	Dominique Martinet <asmadeus@...ewreck.org>,
	K Prateek Nayak <kprateek.nayak@....com>
Cc: akpm@...ux-foundation.org, brauner@...nel.org, dvyukov@...gle.com,
	elver@...gle.com, glider@...gle.com, jack@...e.cz,
	kasan-dev@...glegroups.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk,
	willy@...radead.org, Eric Van Hensbergen <ericvh@...nel.org>,
	Latchesar Ionkov <lucho@...kov.net>, v9fs@...ts.linux.dev
Subject: Re: [syzbot] [fs?] [mm?] INFO: task hung in v9fs_file_fsync

On 08/18, syzbot wrote:
>
> Hello,
>
> syzbot has tested the proposed patch and the reproducer did not trigger any issue:
>
> Reported-by: syzbot+d1b5dace43896bc386c3@...kaller.appspotmail.com
> Tested-by: syzbot+d1b5dace43896bc386c3@...kaller.appspotmail.com
>
> Tested on:
>
> commit:         038d61fd Linux 6.16

And trans_fd.c wasn't changed since 038d61fd...

Dominique, David,

Perhaps you can reconsider the fix that Prateek and I tried to propose
in this thread

	[syzbot] [netfs?] INFO: task hung in netfs_unbuffered_write_iter
	https://lore.kernel.org/all/67dedd2f.050a0220.31a16b.003f.GAE@google.com/

Oleg.
---

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index 339ec4e54778..474fe67f72ac 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -666,7 +666,6 @@ 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;
 	int err;
 	struct p9_trans_fd *ts = client->trans;
 	struct p9_conn *m = &ts->conn;
@@ -686,13 +685,7 @@ 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;
 }