linux-kernel - [PATCH -v5 0/2] printk.devkmsg: Ratelimit it by default

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Date:	Sat, 16 Jul 2016 08:17:43 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...e.de>,
	Dave Young <dyoung@...hat.com>, Franck Bui <fbui@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: [PATCH -v5 0/2] printk.devkmsg: Ratelimit it by default

From: Borislav Petkov <bp@...e.de>

Hi guys,

here's v5 with Andrew's review comments addressed (I hope all).

I've unified the setting names for both sysctl(2) and the kernel cmdline
to "on", "off" and "ratelimit" so that there's no confusion anymore as
to which sysctl number corresponds to what string. This should make
dealing with that option straight-forward.

Also, requested textual expansion regarding the reasoning for the
current design has been added in comments and commit messages.

Thanks.

Changelog:
----------

v4:

sorry for spamming so quickly again and not waiting for a week before
resubmitting but I believe the stuff is ready for 4.8.

So here's v4 with all the minor review comments addressed.

v3:

here's v3 integrating Ingo's comments. The thing is called
printk.devkmsg= or printk_devkmsg now, depending on cmdline option or
sysctl.

v2:

here's v2 with the requested sysctl option kernel.printk_kmsg and
locking of the setting when printk.kmsg= is supplied on the command
line.

Patch 1 is unchanged.

Patch 2 has grown the sysctl addition.

v1:

Rostedt is busy so I took Linus' old patch and Steven's last v2 and
split and extended them with the comments people had on the last thread:

https://lkml.kernel.org/r/20160425145606.598329f2@gandalf.local.home

I hope, at least.

So it is ratelimiting by default, with "on" and "off" cmdline options. I
called the option somewhat a bit shorter too: "printk.kmsg"

The current use cases of this and of which I'm aware are:

* debug the kernel and thus shut up all interfering input from
userspace, i.e. boot with "printk.kmsg=off"

* debug userspace (and by that I mean systemd) by booting with
"printk.kmsg=on" so that the ratelimiting is disabled and the kernel log
gets all the spew.

Thoughts?

Please queue,
thanks.

Borislav Petkov (2):
  ratelimit: Extend to print suppressed messages on release
  printk: Add kernel parameter to control writes to /dev/kmsg

 Documentation/kernel-parameters.txt |   7 ++
 Documentation/sysctl/kernel.txt     |  14 ++++
 include/linux/printk.h              |   9 +++
 include/linux/ratelimit.h           |  38 ++++++++--
 kernel/printk/printk.c              | 143 ++++++++++++++++++++++++++++++++++--
 kernel/sysctl.c                     |   7 ++
 lib/ratelimit.c                     |  10 ++-
 7 files changed, 211 insertions(+), 17 deletions(-)

-- 
2.8.4