From: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Peter Hurley <peter@hurleysoftware.com>,
Jiri Slaby <jirislaby@kernel.org>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Max Filippov <jcmvbkbc@gmail.com>,
David Sterba <dsterba@suse.com>,
Bhaskar Chowdhury <unixbhaskar@gmail.com>,
Igor Matheus Andrade Torrente <igormtorrente@gmail.com>,
nick black <dankamongmen@gmail.com>,
linux-kernel@vger.kernel.org,
syzbot+5f47a8cea6a12b77a876@syzkaller.appspotmail.com,
Marco Elver <elver@google.com>
Subject: Re: [PATCH] vt: Fix sleeping functions called from atomic context
Date: Thu, 18 Nov 2021 18:01:24 +0100 [thread overview]
Message-ID: <1701119.OD4kndUEs1@localhost.localdomain> (raw)
In-Reply-To: <44d83e9c-d8c9-38bf-501c-019b8c2f7b5e@i-love.sakura.ne.jp>
On Thursday, November 18, 2021 1:14:59 PM CET Tetsuo Handa wrote:
> On 2021/11/18 18:38, Fabio M. De Francesco wrote:
> If ->flow.lock were held from only schedulable context, replacing this spinlock with
> a mutex would be possible. But stop_tty() says "may be called from any context" which
> means that we can't use a mutex...
>
> Making do_con_write() no-op when called with IRQs disabled would be the minimal change
> that can silence the syzbot. But this does not fix the regression for drivers/tty/n_hdlc.c
> introduced by f9e053dcfc02b0ad.
>
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -2902,7 +2902,7 @@ static int do_con_write(struct tty_struct *tty, const unsigned char *buf, int co
> struct vt_notifier_param param;
> bool rescan;
>
> - if (in_interrupt())
> + if (in_interrupt() || irqs_disabled())
> return count;
>
> console_lock();
> @@ -3358,7 +3358,7 @@ static void con_flush_chars(struct tty_struct *tty)
> {
> struct vc_data *vc;
>
> - if (in_interrupt()) /* from flush_to_ldisc */
> + if (in_interrupt() || irqs_disabled()) /* from flush_to_ldisc */
> return;
>
> /* if we race with con_close(), vt may be null */
>
For what my opinion is worth, I like the solution by Tetsuo that is reported above.
The bug is real and I suppose that it must be addressed. This seems the most straightforward
and effective way to fix it.
Regards,
Fabio M. De Francesco
> According to scripts/get_maintainer.pl , Greg and Jiri are maintainers for the n_hdlc driver.
> Greg and Jiri, what do you think? Is sacrificing ability to write to consoles when
> n_hdlc_send_frames() is called from __start_tty() path considered tolerable? (Maybe
> OK for now and stable kernels, for nobody was reporting this problem suggests that
> nobody depends on this ability.)
>
> But if we must fix the regression for drivers/tty/n_hdlc.c , we need to use something
> like https://lkml.kernel.org/r/7d851c88-f657-dfd8-34ab-4891ac6388dc@i-love.sakura.ne.jp
> in order to achieve what f9e053dcfc02b0ad meant. That is, extend tty->stopped in order
> to be able to represent "started state (currently indicated by tty->stopped == false)",
> "stopped state (currently indicated by tty->stopped == true)" and "changing state
> (currently impossible due to bool)", but this approach might need to touch many locations,
> and I worry that touching many locations introduces some oversight bugs.
>
>
next prev parent reply other threads:[~2021-11-18 17:01 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-16 14:49 [PATCH] vt: Fix sleeping functions called from atomic context Fabio M. De Francesco
2021-11-16 14:58 ` Greg Kroah-Hartman
2021-11-16 15:35 ` Fabio M. De Francesco
2021-11-16 16:59 ` Greg Kroah-Hartman
2021-11-16 17:28 ` Fabio M. De Francesco
2021-11-17 8:23 ` Fabio M. De Francesco
2021-11-17 8:54 ` Greg Kroah-Hartman
2021-11-17 10:51 ` Tetsuo Handa
2021-11-18 8:31 ` Fabio M. De Francesco
2021-11-18 9:38 ` Fabio M. De Francesco
2021-11-18 12:14 ` Tetsuo Handa
2021-11-18 17:01 ` Fabio M. De Francesco [this message]
2021-11-19 14:55 ` [PATCH] tty: vt: make do_con_write() no-op if IRQ is disabled Tetsuo Handa
2021-12-01 13:40 ` Tetsuo Handa
2021-12-01 14:20 ` Greg Kroah-Hartman
2021-12-01 19:05 ` Linus Torvalds
2021-12-02 15:40 ` Tetsuo Handa
2021-12-02 18:35 ` Linus Torvalds
2021-12-03 5:03 ` Jiri Slaby
2021-12-03 11:00 ` Fabio M. De Francesco
2021-12-03 12:32 ` Tetsuo Handa
2021-12-03 14:51 ` Fabio M. De Francesco
2021-11-17 12:38 ` [PATCH] vt: Fix sleeping functions called from atomic context Fabio M. De Francesco
2021-11-17 1:55 ` Tetsuo Handa
2021-11-17 7:02 ` Fabio M. De Francesco
2021-12-06 11:44 ` [PATCH] tty: n_hdlc: make n_hdlc_tty_wakeup() asynchronous Tetsuo Handa
2021-12-06 18:07 ` Linus Torvalds
2021-12-09 13:18 ` Tetsuo Handa
2021-12-15 11:52 ` [PATCH (resend)] " Tetsuo Handa
2021-12-06 19:06 ` [PATCH] " Fabio M. De Francesco
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