linux-kernel - Re: [PATCH] init/main.c: check for null pointer before calling initcall

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Message-ID: <alpine.DEB.2.20.1710272139420.1922@nanos>
Date:   Fri, 27 Oct 2017 21:43:02 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Abderrahmane Benbachir <abderrahmane.benbachir@...ymtl.ca>
cc:     David Daney <ddaney@...iumnetworks.com>,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        akpm@...ux-foundation.org, keescook@...omium.org, jeyu@...hat.com,
        rostedt@...dmis.org, mhocko@...e.com, viresh.kumar@...aro.org,
        thomas.lendacky@....com
Subject: Re: [PATCH] init/main.c: check for null pointer before calling
 initcall

On Fri, 27 Oct 2017, Abderrahmane Benbachir wrote:
> David Daney <ddaney@...iumnetworks.com> a écrit :
> 
> > On 10/27/2017 11:22 AM, Thomas Gleixner wrote:
> > > On Fri, 27 Oct 2017, David Daney wrote:
> > > 
> > > > On 10/27/2017 09:47 AM, Abderrahmane Benbachir wrote:
> > > > > Simple check to prevent kernel panic when initcall does not exit
> > > > 
> > > > Interesting, under what circumstances do you observe the panic?
> > > > 
> > > > It would be best to include this information in the patch changelog.
> > > 
> > > device_initcall(NULL);
> > > 
> > > might do that, but then it rightfully crashes on boot.
> > > 
> > 
> > That was kind of my point.  The module loader case already checks for a
> > non-NULL pointer, and any NULLs in the in-kernel initializer tables would
> > indicate a bigger problem that should be fixed instead.
> > 
> > David Daney
> 
> But this code can still be written :
> 
> static initcall_t __initcall_mymod \
>   __used __section(".initcall6.init") = NULL;

You can write that, but it's simply wrong and abusing the initcall
system. As I said, the system rightfully crashes.

There are sane ways to do conditional initialization from within a fixed
initcall.

Thanks,

	tglx