Re: [PATCH 00/50] Add log level to show_stack() - Russell King

From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Peter Zijlstra <peterz@infradead.org>
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Subject: Re: [PATCH 00/50] Add log level to show_stack()
Date: Wed, 6 Nov 2019 23:25:13 +0000	[thread overview]
Message-ID: <20191106232512.GU25745@shell.armlinux.org.uk> (raw)
In-Reply-To: <20191106203440.GH3079@worktop.programming.kicks-ass.net>

On Wed, Nov 06, 2019 at 09:34:40PM +0100, Peter Zijlstra wrote:
> I suppose I'm surprised there are backtraces that are not important.
> Either badness happened and it needs printing, or the user asked for it
> and it needs printing.

Or utterly meaningless.

> Perhaps we should be removing backtraces if they're not important
> instead of allowing to print them as lower loglevels?

Definitely!  WARN_ON() is well overused - and as is typical, used
without much thought.  Bound to happen after Linus got shirty about
BUG_ON() being over used.  Everyone just grabbed the next nearest thing
to assert().

As a kind of example, I've recently come across one WARN_ON() in a
driver subsystem (that shall remain nameless at the moment) which very
likely has multiple different devices on a platform.  The WARN_ON()
triggers as a result of a problem with the hardware, but because it's a
WARN_ON(), you've no idea which device has a problem.  The backtrace is
mostly meaningless.  So you know that a problem has occurred, but the
kernel prints *useless* backtrace to let you know, and totally omits
the *useful* information.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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