linux-kernel - Re: [PATCH v2] printk: make sure to print log on console.

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Message-ID: <20180608083906.fwx3r3y2pxtv3ga6@pathway.suse.cz>
Date:   Fri, 8 Jun 2018 10:39:06 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Maninder Singh <maninder1.s@...sung.com>
Cc:     sergey.senozhatsky@...il.com, rostedt@...dmis.org,
        linux-kernel@...r.kernel.org, a.sahrawat@...sung.com,
        pankaj.m@...sung.com, v.narang@...sung.com
Subject: Re: [PATCH v2] printk: make sure to print log on console.

On Fri 2018-06-01 14:26:42, Maninder Singh wrote:
> This patch make sure printing of log on console if loglevel
> at time of storing log is less than current console loglevel.
> 
> @why
> In SMP printk can work asynchronously, logs can be missed on console
> because it checks current log level at time of console_unlock,
> not at time of storing logs.
> 
> func()
> {
> ....
> ....
>         console_verbose();  // user wants to have all the logs on console.
>         pr_alert();
> 	dump_backtrace(); //prints with default loglevel.
>         ...
>         console_silent(); // stop all logs from printing on console.
> }
> 
> Now if console_lock was owned by another process, the messages might
> be handled after the consoles were silenced.

It might make sense to document the limitations reported by
Sergey. I mean to add something like:

"There are still some corner cases where this patch is not enough,
for example, when the messages are flushed later from printk_safe
buffers or when there are races between console_verbose() and
console_silent() callers."


> reused flag LOG_NOCONS as its usage is gone long back.
> (5c2992ee7fd8a29d04125dc0aa3522784c5fa5eb)
> 
> Signed-off-by: Vaneet Narang <v.narang@...sung.com>
> Signed-off-by: Maninder Singh <maninder1.s@...sung.com>

Anyway. the patch helps in many situations and it is a step in the right
direction:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr

PS: There is no need to resend the patch. I could update the commit
message when pushing the patch. I am just going to wait a bit for
other potential reviewers.