linux-kernel - Re: [syzbot] possible deadlock in console_lock_spinning

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Message-ID: <YrA8vzVjxJIrZFBz@google.com>
Date:   Mon, 20 Jun 2022 18:24:15 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        syzbot <syzbot+3cc1054e15babd5f4cd2@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, glider@...gle.com,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        john.ogness@...utronix.de, linux-kernel@...r.kernel.org,
        npiggin@...il.com, pmladek@...e.com, rdunlap@...radead.org,
        rostedt@...dmis.org, swboyd@...omium.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] possible deadlock in console_lock_spinning_enable (2)

On (22/06/20 10:16), Dmitry Vyukov wrote:
> On Mon, 20 Jun 2022 at 07:44, Sergey Senozhatsky
> <senozhatsky@...omium.org> wrote:
> >
> > On (22/06/18 20:47), syzbot wrote:
> > > syzbot suspects this issue was fixed by commit:
> > >
> > > commit faebd693c59387b7b765fab64b543855e15a91b4
> > > Author: John Ogness <john.ogness@...utronix.de>
> > > Date:   Thu Apr 21 21:22:36 2022 +0000
> > >
> > >     printk: rename cpulock functions
> >
> > I'd rather guess that it was console kthread patch that fixed the problem.
> 
> Hi Sergey,
> 
> Do you mean this commit:
> 
> author: John Ogness 2022-04-21 23:28:48 +0206
> printk: add kthread console printers
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=09c5ba0aa2fcfdadb17d045c3ee6f86d69270df7

Yes, I'd assume so. The patch removes

	tty -> printk -> tty

which re-enters tty in unsafe manner, and replaces it with

	tty -> printk -> wake_up console printer