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

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Message-ID: <20171027185340.Horde.lrfWRcBHRmhKk906QJGixBF@www.imp.polymtl.ca>
Date:   Fri, 27 Oct 2017 18:53:40 +0000
From:   Abderrahmane Benbachir <abderrahmane.benbachir@...ymtl.ca>
To:     David Daney <ddaney@...iumnetworks.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, 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


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;

In fact, I'm using the code below to assign at runtime (dynamically) which
function to be executed or not.