linux-kernel - Re: [PATCH 2/2] task_work: check callback if it's NULL

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Date:	Fri, 15 Mar 2013 09:43:00 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	li guang <lig.fnst@...fujitsu.com>
CC:	Oleg Nesterov <oleg@...hat.com>, <viro@...iv.linux.org.uk>,
	<edumazet@...gle.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] task_work: check callback if it's NULL

On 2013/3/15 9:26, li guang wrote:
> 在 2013-03-15五的 09:01 +0800，Li Zefan写道：
>> On 2013/3/15 8:20, li guang wrote:
>>> 在 2013-03-14四的 15:43 +0100，Oleg Nesterov写道：
>>>> On 03/14, liguang wrote:
>>>>>
>>>>> Signed-off-by: liguang <lig.fnst@...fujitsu.com>
>>>>> ---
>>>>>  kernel/task_work.c |    3 ++-
>>>>>  1 files changed, 2 insertions(+), 1 deletions(-)
>>>>>
>>>>> diff --git a/kernel/task_work.c b/kernel/task_work.c
>>>>> index 0bf4258..f458b08 100644
>>>>> --- a/kernel/task_work.c
>>>>> +++ b/kernel/task_work.c
>>>>> @@ -75,7 +75,8 @@ void task_work_run(void)
>>>>>
>>>>>  		do {
>>>>>  			next = work->next;
>>>>> -			work->func(work);
>>>>> +			if (unlikely(work->func))
>>>>> +				work->func(work);
>>>>
>>>> Why?
>>>>
>>>> Oleg.
>>>>
>>>
>>> can we believe a callback always be call-able?
>>> can it happened to be 0? e.g. wrong initialized.
>>> of course, we can complain the caller, be why don't
>>> we easily make it more safer?
>>>
>>
>> Because you're not making things safer, but your're trying
>> to cover up bugs...
>>
> 
> Oh, that's a little harsh to a normal programmer like me :-)
> for it seems you are asking me to be coding without any bug.
> are you? or it is the theory of kernel coding?
> 

And you make a bug, and you want the kernel to cover up the bug
instead of crash on a null pointer deref so you'll know you've
made a bug?

Why we check if a callback is NULL before calling it? Because
it's allowed to be. Why we don't check if a callback is NULL?
Because it's not supposed to be.

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