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

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Message-ID: <20180625142758.ourdvfid3aymgvan@pathway.suse.cz>
Date:   Mon, 25 Jun 2018 16:27:58 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Maninder Singh <maninder1.s@...sung.com>,
        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 Wed 2018-06-20 10:55:25, Sergey Senozhatsky wrote:
> On (06/19/18 12:52), Petr Mladek wrote:
> > > But when I set /sys/module/printk/parameters/ignore_loglevel I naturally
> > > expect it to take an immediate action. Without waiting for the consoles
> > > to catch up and to discard N messages [if the consoles were behind the
> > > logbuf head].
> > 
> > Yeah, I understand this view. I thought about it as well. But did you
> > ever needed this behavior in the real life?
> >
> > I personally changed ignore_loglevel only before I wanted to reproduce a
> > bug. Then it would be perfectly fine to handle it only in
> > vprintk_emit(). In fact, it would be even better because it would
> > affect only messages that happened after I triggered the bug.
> 
> So maybe the patch can stand the way it is, after all. JFI, still haven't
> seen those "helps in real life a lot" examples, tho.

I have personally seen these races when testing printk in NMI. I
combined iptables logging, ping -f and sysrq-l. I am not sure
how often they happen in the real life but I could understand
that it might be annoying.

This patch goes in the right direction and nobody really blocks
it. Therefore I pushed it into printk.git, branch for-4.19.

Best Regards,
Petr