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Subject: Re: [PATCHv2 2/4] tty: Hold tty_ldisc_lock() during tty_reopen()
To:     Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Dmitry Safonov <dima@arista.com>
Cc:     linux-kernel@vger.kernel.org,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Daniel Axtens <dja@axtens.net>,
        Dmitry Vyukov <dvyukov@google.com>,
        Michael Neuling <mikey@neuling.org>,
        Mikulas Patocka <mpatocka@redhat.com>,
        Nathan March <nathan@gt.net>,
        =?UTF-8?B?UGFzaSBLw6Rya2vDpGluZW4=?= <pasik@iki.fi>,
        Peter Hurley <peter@hurleysoftware.com>,
        Tan Xiaojun <tanxiaojun@huawei.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        syzbot+3aa9784721dfb90e984d@syzkaller.appspotmail.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org
References: <20180903165257.29227-1-dima@arista.com>
 <20180903165257.29227-3-dima@arista.com> <20180904015139.GA4251@jagdpanzerIV>
From:   Jiri Slaby <jslaby@suse.com>
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Message-ID: <7e62b122-3b9e-dc46-d99f-9055bb67d670@suse.com>
Date:   Tue, 4 Sep 2018 08:30:50 +0200
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On 09/04/2018, 03:51 AM, Sergey Senozhatsky wrote:
> On (09/03/18 17:52), Dmitry Safonov wrote:
>>
>> We've seen the following crash on v4.9.108 stable:
>>
>> BUG: unable to handle kernel paging request at 0000000000002260
>> IP: [..] n_tty_receive_buf_common+0x5f/0x86d
>> Workqueue: events_unbound flush_to_ldisc
>> Call Trace:
>>  [..] n_tty_receive_buf2
>>  [..] tty_ldisc_receive_buf
>>  [..] flush_to_ldisc
>>  [..] process_one_work
>>  [..] worker_thread
>>  [..] kthread
>>  [..] ret_from_fork
>>
>> tty_ldisc_reinit() should be called with ldisc_sem hold for writing,
>> which will protect any reader against line discipline changes.
>>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: Jiri Slaby <jslaby@suse.com>
>> Cc: stable@vger.kernel.org # depends on commit b027e2298bd5 ("tty: fix
>> data race between tty_init_dev and flush of buf")
> 
> I believe there's a "Fixes" tag for that
> 
> Fixes: b027e2298bd5 ("tty: fix data race between tty_init_dev and flush of buf")
> Cc: stable@vger.kernel.org

Nope, it would be translated as:
Backport-first: b027e2298bd5
:)

thanks,
-- 
js
suse labs