linux-kernel - Re: [PATCH] kernel/rcutorture.c: use scnprintf() instead of sprintf()

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Date:	Tue, 15 Oct 2013 20:32:41 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	josh@...edesktop.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel/rcutorture.c: use scnprintf() instead of sprintf()

On 10/15/2013 04:26 PM, Paul E. McKenney wrote:
> On Tue, Oct 15, 2013 at 09:51:42AM +0800, Chen Gang wrote:
>>> One simple way: using snprintf() instead of scnprintf() in the related
>>> printing functions. Then call them with "buffer == NULL" to get buffer
>>> size, next allocate it and call it again ...
>>
>> Oh, this simple way assumes the printing contents will not be changed
>> during the 2 calls.
> 
> Indeed.  But can you make use of nr_cpu_ids, which is set at boot time
> to the the maximum number of CPUs that the particular booting system
> will ever be able to contain?  Keep in mind that you know the maximum
> number of digits that an unsigned long will print in 32-bit and 64-bit
> systems.
> 

Yeah, that is a way for it. It seems you (related maintainer) like
additional fix for it.

Hmm... I will try within this week (although I don't think it is quite
necessary to me).

:-)

>>> Hmm... it is only a test module, is it worth enough to try to make it
>>> avoid truncation? If some members (quite few members) find truncation,
>>> they can simply extend maximize buffer to avoid it when testing.
>>>
>>> But if we do not fix this bug, when memory overflow, the OS may not stop
>>> immediately, then it will/may lead the testers to face various amazing
>>> things (which is not quite easy to find root cause).
> 
> It might cause strange symptoms, but it is not bad practice to try
> it anyway, especially when the code is unfamiliar.  After all, if the
> strange systems appear on memory overflow, but do not appear if there
> is no memory overflow, you have a pretty good idea what the cause .
> Besides, there might be some other mechanism to prevent the problem.
> Of course, there is no such mechanism in this particular case, but in
> general it is more efficient to find that out quickly then to spend time
> designing a solution that is not needed.

Excuse me, my English is not quite well, I am not quite understand your
meaning.

I guess your meaning is: "after find a simple/acceptable solution, we
can think of more, it may be more efficient".

If what I guess is correct, It is OK to me -- since at least, it is not
an 'urgent' thing (for 'important' thing, your idea is more efficient,
although for 'urgent' thing, it is not).


Thanks.
-- 
Chen Gang
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