linux-kernel - Re: [PATCH 05/13] tty: remove tty

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Message-ID: <92b1f39d-9c9c-c319-a351-f3cb9a1c0497@i-love.sakura.ne.jp>
Date:   Thu, 8 Apr 2021 22:47:21 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jirislaby@...nel.org>, linux-kernel@...r.kernel.org,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH 05/13] tty: remove tty_warn()

On 2021/04/08 21:51, Greg Kroah-Hartman wrote:
> Remove users of tty_warn() and replace them with calls to dev_warn()
> which provides more information about the tty that has the error and
> uses the standard formatting logic.

Ouch. This series would be good for clean up, but this series might be
bad for handling lockdep warning syzbot is reporting.

Since tty_warn() is using plain printk(), we can avoid lockdep warning by
using printk_deferred(). If we use dev_warn() instead, we need to modify
__dev_printk() to use printk_deferred(), which means that all dev_*() users
are affected by this change.

Also, we need to modify dev_printk_emit()/dev_vprintk_emit() callers to embed
loglevel into the format string so that we pass LOGLEVEL_SCHED to vprintk_emit() ...
maybe just change from "if (!in_sched)" to "if (!in_sched && !dev_info)" instead ?

Also, dev_vprintk_emit() need to start calling defer_console_output()
after returning from vprintk_emit() in order to behave like printk_deferred().

I'm not sure whether this change is safe.