linux-kernel - Re: [syzbot] [kernel?] possible deadlock in console_flush

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Message-ID: <895193c7-1339-45b3-99fa-6fc804040a3c@I-love.SAKURA.ne.jp>
Date: Wed, 27 Mar 2024 23:25:14 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: John Ogness <john.ogness@...utronix.de>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        John Fastabend <john.fastabend@...il.com>
Cc: syzbot <syzbot+f78380e4eae53c64125c@...kaller.appspotmail.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [syzbot] [kernel?] possible deadlock in console_flush_all (2)

On 2024/03/27 20:05, John Ogness wrote:
> The printk rework (which is not yet fully mainline) will correctly
> handle this context.
> 
> As to the patch [0] you suggested, it would be more appropriate to
> perform deferred_enter/_exit *within* the locked critical section. But
> we really only want these whack-a-mole workarounds for cases that can
> occur in a non-bug situation. IMHO this is not such a case and falls
> into the category of "known problem, the rework will handle it".
> 
> John Ogness
> 
> [0] https://syzkaller.appspot.com/text?tag=Patch&x=121c92fe180000
> 

Since the cause of current flood of lockdep reports is already explained
in https://syzkaller.appspot.com/bug?extid=c4f4d25859c2e5859988 , we don't
need [0] for now. But it is unfortunate that the message which explains
what went wrong cannot be reported due to reporting console_lock dependency.
Therefore, I intend [0] as a workaround for a bug situation. We can revert [0]
after the printk rework completed.