linux-kernel - Re: [PATCH] printk: git rid of [sched_delayed] message for printk

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 20 Sep 2014 20:08:00 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Joe Perches <joe@...ches.com>, Jan Kara <jack@...e.cz>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] printk: git rid of [sched_delayed] message for
 printk_deferred

On Sat, Sep 20, 2014 at 12:30:01PM -0400, Steven Rostedt wrote:
> On Sat, 20 Sep 2014 09:10:47 -0700
> Joe Perches <joe@...ches.com> wrote:
> 
> > On Sat, 2014-09-20 at 17:47 +0200, Peter Zijlstra wrote:
> > > On a whole, printk() is entirely useless for debugging these days, its
> > > far too fragile/unreliable to be taken seriously so I really don't care
> > > on that point either.
> > 
> > That's unfortunate.
> > 
> > Care to enumerate the issues that you believe make
> > printk too fragile/unreliable for debugging?
> 
> I seldom use printk these days. It's far too limited in its uses. For
> one, most things worth debugging happen thousands of times a second,
> and printk will just slow things down to a crawl if it is used.
> Another, is that it can not be used in most critical sections (NMI
> handlers and anything that deals with the scheduler). Also, as it no
> longer blocks when another CPU is doing a printk, a bug can happen
> which crashes the system and the output of that bug will never get
> printed due to the delayed output from another CPU having the console
> lock.

If you're trying to debug a dying machine the early_serial_console which
basically only does a stream of OUTBs to the right port is the only
reliable thing. For anything else, trace_printk().

Now all I need to figure out is how to keep suspend from killing the
early_serial_console setup :-)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/