linux-kernel - Re: [syzbot] [kernel?] KCSAN: data-race in __fput / __tty

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Message-ID: <0a23d945-0502-6330-d9ef-a6f8dd3a68e2@I-love.SAKURA.ne.jp>
Date:   Sat, 22 Apr 2023 01:02:09 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+b7c3ba8cdc2f6cf83c21@...kaller.appspotmail.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Cc:     linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [kernel?] KCSAN: data-race in __fput / __tty_hangup (4)

On 2023/04/22 0:12, Tetsuo Handa wrote:
> __fput(file) is called when the last reference to file is released.
> Since __tty_hangup() traverses tty->tty_files under tty->files_lock,
> tty_add_file() needs to hold a ref before adding to tty->tty_files
> in order to defer concurrent __fput() by other threads?

Hmm, this did not work; get_file() prevents tty_release().