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

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Message-ID: <20181218111701.GA32522@jagdpanzerIV>
Date:   Tue, 18 Dec 2018 20:17:01 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Borislav Petkov <bp@...en8.de>,
        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 (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...

	-ss