linux-kernel - Re: [RFC] printk/sysrq: Don't play with console

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Message-ID: <20190612120012.mmokgz4yybywfs26@pathway.suse.cz>
Date:   Wed, 12 Jun 2019 14:00:12 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Dmitry Safonov <dima@...sta.com>, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: Re: [RFC] printk/sysrq: Don't play with console_loglevel

On Wed 2019-06-12 17:36:43, Sergey Senozhatsky wrote:
> On (06/06/19 09:10), Petr Mladek wrote:
> > Just to be sure. I wanted to say that I like the idea with
> > KERN_UNSUPRESSED. So, I think that we are on the same page.
> 
> I understand. All I wanted to say is that KERN_UNSUPRESSED is
> per-message, while the most interesting (and actually broken)
> cases, IMHO, are per-context, IOW things like this one
> 
> 	console_loglevel = NEW
> 	foo()
> 	  dump_stack()
> 	     printk
> 	     ...
> 	     printk
> 	console_loglevel = OLD
> 
> KERN_UNSUPRESSED does not help here. We probably can't convert
> dump_stack() to KERN_UNSUPRESSED.

I agree. I take KERN_UNSUPRESSED like a nice trick how to pass
the information about the unsupressed printk context via
printk_safe and printk_nmi per-CPU buffers.

The single line in sysrq __handle_sysrq() seems to be the only
location where KERN_UNSUPRESSED can be used directly.

Best Regards,
Petr