linux-kernel - Re: [RFC][PATCH] printk: increase devkmsg write() ratelimit

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Message-ID: <20181218114709.GF7485@zn.tnic>
Date:   Tue, 18 Dec 2018 12:47:09 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [RFC][PATCH] printk: increase devkmsg write() ratelimit

On Tue, Dec 18, 2018 at 08:17:01PM +0900, Sergey Senozhatsky wrote:
> On (12/18/18 11:48), Peter Zijlstra wrote:
> > > I know that there is a "kernel.printk_devkmsg" interface; do we
> > > expect every systemd-enabled distro to find that out and to tweak
> > > kernel.printk_devkmsg or shall we change the default devkmsg
> > > ratelimit instead?
> > 
> > How about we complain to systemd instead?
> 
> We certainly can. As far as I understand, they log shutdown events
> (including errors and warnings): what they kill, what they stop,
> what they umount, etc. The more partitions, services are running
> (I guess), the more things they need to umount, kill, stop; hence,
> the more messages. I kinda can imagine what they will answer ;)
> 
> The below (and a bunch of other) messages are getting ratelimited.
> I'm not sure what will happen should any of those steps fail and
> print warning-s. My guess would be that we probably can ratelimit
> those warnings:
> 
> ...
>  systemd[1]: Unmounting /home...
>  systemd[1]: Unmounting Temporary Directory (/tmp)...
>  systemd[1]: Unmounted Temporary Directory (/tmp).
>  systemd[1]: Stopped target Swap.
>  systemd[1]: Unmounted /boot.
>  systemd[1]: Stopped File System Check on /dev/disk/by-uuid/a0737dff-e797-44f0-aea7-d0df1107ff63.
>  systemd[1]: Stopped File System Check on /dev/disk/by-uuid/5d773b72-e200-4d11-a219-176d62a16d8d.
>  systemd[1]: Unmounted /home.
>  systemd[1]: Stopped File System Check on /dev/disk/by-uuid/35319ddc-9b92-4ab0-aaa4-9922db636a5e.
>  systemd[1]: Unmounted /media/edev.
>  systemd[1]: Stopped File System Check on /dev/disk/by-uuid/da00daaf-5601-4531-912e-bd69103b379d.
>  systemd[1]: Unmounted /media/dump.
>  systemd[1]: Reached target Unmount All Filesystems.
>  systemd[1]: Stopped File System Check on /dev/disk/by-uuid/b52da2df-161b-4c33-b700-277d95b9672f.
>  systemd[1]: Removed slice system-systemd\x2dfsck.slice.
>  systemd[1]: Stopped target Local File Systems (Pre).
>  systemd[1]: Stopped Create Static Device Nodes in /dev.
>  systemd[1]: Stopped Create System Users.
>  systemd[1]: Stopped Remount Root and Kernel File Systems.
>  systemd[1]: Reached target Shutdown.
>  systemd[1]: Reached target Final Step.
>  systemd[1]: Starting Reboot...

And we wanna see all those "very useful" messages in dmesg because...?

-- 
Regards/Gruss,
    Boris.

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