From: Dominique Martinet <asmadeus@codewreck.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: syzbot <syzbot+c0dc46208750f063d0e0@syzkaller.appspotmail.com>,
v9fs@lists.linux.dev, dhowells@redhat.com, jlayton@kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
netfs@lists.linux.dev, syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [netfs?] kernel BUG in folio_unlock (3)
Date: Fri, 21 Feb 2025 07:05:46 +0900 [thread overview]
Message-ID: <Z7enOheevlbS1xpH@codewreck.org> (raw)
In-Reply-To: <Z7dVOaTWTVCojNzr@casper.infradead.org>
Matthew Wilcox wrote on Thu, Feb 20, 2025 at 04:15:53PM +0000:
> On Thu, Feb 20, 2025 at 08:00:24AM -0800, syzbot wrote:
> > ------------[ cut here ]------------
> > kernel BUG at mm/filemap.c:1499!
>
> Tried to unlock a folio that wasn't locked.
>
> The entire log is interesting:
>
> https://syzkaller.appspot.com/x/log.txt?x=12af2fdf980000
>
> It injects a failure which hits p9_tag_alloc() (so adding the 9p people
> to the cc)
9p is calling iov_iter_revert() in p9_client_write() on failure, but at
this point of the failure copy_from_iter_full (which advanced the iter)
wasn't called yet because the format processing happens after
allocation...
This was changed by Al Viro in 2015 so it's a "fairly old" bug, but it's
a bug on 9p side alright - thanks for the cc
Now to figure out how to decide if we want to revert or not... I
honestly don't have any bright idea, but I don't know the iov API well
at all -- perhaps it's possible to copy without advancing and only
advance the iov if IO worked?
--
Dominique Martinet | Asmadeus
next prev parent reply other threads:[~2025-02-21 2:51 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-02-20 16:00 [syzbot] [netfs?] kernel BUG in folio_unlock (3) syzbot
2025-02-20 16:15 ` Matthew Wilcox
2025-02-20 22:05 ` Dominique Martinet [this message]
2025-02-21 23:35 ` Hillf Danton
2025-02-21 23:58 ` syzbot
2025-02-26 8:41 ` David Howells
2025-05-31 23:20 ` syzbot
2025-06-01 0:26 ` Matthew Wilcox
2025-06-11 14:08 ` Aleksandr Nogikh
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