linux-kernel - Re: [PATCH] kref: Avoid null pointer dereference after WARN

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Message-ID: <20170628112604.GA5234@dhcp22.suse.cz>
Date:   Wed, 28 Jun 2017 13:26:04 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Daniel Micay <danielmicay@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kref: Avoid null pointer dereference after WARN

On Tue 27-06-17 12:29:39, Andi Kleen wrote:
> On Tue, Jun 27, 2017 at 09:11:28PM +0200, Jason A. Donenfeld wrote:
[...]
> > The bigger question, though, is the value of these checks in the first
> > place. Has anybody written a coccinelle check to look into this
> > statically? Has it historically been a useful thing for driver
> > developers to have? Is it good defense in depth or is it overkill? At
> > the very least, the original authors of kref thought a WARN_ON was
> > warranted, which means probably a BUG_ON is a sensible fix, until
> > somebody does the work of investigating these more careful questions.
> 
> Right that's the question that should have been answered before
> this patch.
> 
> I don't think it was ever intended to be a defense, just as a hint
> for driver developers.
> 
> My suspicion is that they're mostly useless.

Completely agreed here!
-- 
Michal Hocko
SUSE Labs