linux-kernel - Re:Re: [PATCH v2] drm/amdkfd: Fix memory leaks according to error branches

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Date:   Sat, 20 Jun 2020 19:16:55 +0800 (GMT+08:00)
From:   Bernard <bernard@...o.com>
To:     Julia Lawall <julia.lawall@...ia.fr>
Cc:     Markus Elfring <Markus.Elfring@....de>, opensource.kernel@...o.com,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        Felix Kühling <Felix.Kuehling@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>
Subject: Re:Re: [PATCH v2] drm/amdkfd: Fix memory leaks according to error branches



From: Julia Lawall <julia.lawall@...ia.fr>
Date: 2020-06-20 17:37:19
To:  Markus Elfring <Markus.Elfring@....de>
Cc:  Bernard Zhao <bernard@...o.com>,opensource.kernel@...o.com,amd-gfx@...ts.freedesktop.org,dri-devel@...ts.freedesktop.org,kernel-janitors@...r.kernel.org,linux-kernel@...r.kernel.org,Alex Deucher <alexander.deucher@....com>,"Christian König" <christian.koenig@....com>,"Felix Kühling" <Felix.Kuehling@....com>,Daniel Vetter <daniel@...ll.ch>,David Airlie <airlied@...ux.ie>
Subject: Re: [PATCH v2] drm/amdkfd: Fix memory leaks according to error branches>
>
>On Sat, 20 Jun 2020, Markus Elfring wrote:
>
>> > The function kobject_init_and_add alloc memory like:
>> > kobject_init_and_add->kobject_add_varg->kobject_set_name_vargs
>> > ->kvasprintf_const->kstrdup_const->kstrdup->kmalloc_track_caller
>> > ->kmalloc_slab, in err branch this memory not free. If use
>> > kmemleak, this path maybe catched.
>> > These changes are to add kobject_put in kobject_init_and_add
>> > failed branch, fix potential memleak.
>>
>> I suggest to improve this change description.
>>
>> * Can an other wording variant be nicer?
>
>Markus's suggestion is as usual extremely imprecise.  However, I also find
>the message quite unclear.
>
>It would be good to always use English words.  alloc and err are not
>English words.  Perhaps most people will figure out what they are
>abbreviations for, but it would be better to use a few more letters to
>make it so that no one has to guess.
>
>Then there are a bunch of things that are connected by arrows with no
>spaces between them.  The most obvious meaning of an arrow with no space
>around it is a variable dereference.  After spending some mental effort,
>one can realize that that is not what you mean here.  A layout like:
>
>   first_function ->
>     second_function ->
>       third_function
>
>would be much more readable.
>
>I don't know what "this patch maybe catched" means.  Is "catched" supposed
>to be "caught" or "cached"?  Overall, the sentence could be "Kmemleak
>could possibly detect this issue", or something like that.  But I don't
>know what this means.  Did you detect the problem with kmemleak?  if you
>did not detect the problem with kmemleak, and overall you don't know
>whether kmemleak would detect the bug or not, is this information useful
>at all for the patch?

Hi:

Kmemleak detected a memory leak as below:
kobject_init_and_add->
	kobject_add_varg->
		kobject_set_name_vargs->
			kvasprintf_const->
				kstrdup_const->
					kstrdup->
						kmalloc_track_caller->
							kmalloc_slab
	
If kobject_init_and_add is called, but kobject_put is not called in the error branch.
This will be detected by kmemleak.

BR//Bernard

>"These changes are to" makes a lot of words with no information.  While it
>is perhaps not necessary to slavishly follow the rule about using the
>imperative, if it is convenient to use the imperative, doing so eliminates
>such meaningless phrases.
>
>memleak is also not an English word.  Memory leak is only a few more
>characters, and doesn't require the reader to make the small extra effort
>to figure out what you mean.
>
>julia
>
>>
>> * Will the tag “Fixes” become helpful for the commit message?
>>
>> Regards,
>> Markus
>>