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

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Message-ID: <aKOhQcVwLd1Kvt6N@codewreck.org>
Date: Tue, 19 Aug 2025 06:55:13 +0900
From: Dominique Martinet <asmadeus@...ewreck.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: syzbot <syzbot+d1b5dace43896bc386c3@...kaller.appspotmail.com>,
	David Howells <dhowells@...hat.com>,
	K Prateek Nayak <kprateek.nayak@....com>, 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
Subject: Re: [syzbot] [fs?] [mm?] INFO: task hung in v9fs_file_fsync

Hi Oleg,

Oleg Nesterov wrote on Mon, Aug 18, 2025 at 02:56:26PM +0200:
> On 08/18, syzbot wrote:
> > syzbot has tested the proposed patch and the reproducer did not trigger any issue:

(I hate that syzbot identified "hung in v9fs_file_fsync" but doesn't
bother to Cc 9p folks... all the time..)

> 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/

I've re-read that thread, and I still think this must be a problem
specific to syzbot doing obviously bogus things (e.g. replying before
request, or whatever it is this particular repro is doing), but I guess
your patch is also sane enough and the 9p optimization is probably not
really needed here

Please resend as a proper patch, and I'll just run some quick check (and
a trivial benchmark) and pick it up

Thanks,
-- 
Dominique Martinet | Asmadeus