linux-kernel - Re: [PATCHv7 5/8] printk: report lost messages in printk safe/nmi contexts

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Date:   Fri, 3 Feb 2017 10:57:57 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        Calvin Owens <calvinowens@...com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Hurley <peter@...leysoftware.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv7 5/8] printk: report lost messages in printk safe/nmi
 contexts

On (02/02/17 09:34), Steven Rostedt wrote:
> On Thu, 2 Feb 2017 11:02:57 +0900
> Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> wrote:
> 
> > On (02/01/17 11:37), Steven Rostedt wrote:
> > > This looks fine, but I'm curious if you tested it. That is, added a
> > > bunch of printks to overflow the buffer. IIRC, I did it to the original
> > > nmi code. If you haven't you may want to just to make sure it works. I
> > > can also test it too if I get some time.
> > 
> > Hello Steven,
> > 
> > yes, I have tested it on my x86 box.
> > 
> 
> Please note how you tested it in your change log. It's not really a
> requirement, and you don't really have to do it. But it helps people
> have warm fuzzies about the code. I'm trying to do this in the future
> in my own work too.

well. sure, no objections, but in this particular case it's hardly possible
to hit all of those problems within a reasonable time. so what I did was just
a bunch of dirty hacks to provoke the problems. something like this

	extern int XXX;

	vprintk_emit()
	{
		spin_lock(&logbuf_lock);

			//
			// in various places
			//
			if (XXX == 1) {
				WARN_ON(1);
			}

		spin_unlock(&logbuf_lock);
	}

and I set/clear that XXX from one of sysfs attrs... yeah, I know...
but it does what I want. so I'm not really sure I want to note this
in the change log. am I wrong?

	-ss