linux-kernel - Re: [PATCH] perf_event: fix error handling path

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Message-ID: <4D010C9D.6020005@linux.vnet.ibm.com>
Date:	Thu, 09 Dec 2010 09:06:37 -0800
From:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
To:	jovi zhang <bookjovi@...il.com>
CC:	Thiago Farina <tfransosi@...il.com>, a.p.zijlstra@...llo.nl,
	paulus@...ba.org, mingo@...e.hu, acme@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf_event: fix error handling path

On 12/07/2010 05:51 PM, jovi zhang wrote:
> On Mon, Dec 6, 2010 at 9:59 AM, jovi zhang<bookjovi@...il.com>  wrote:
>> On Sun, Dec 5, 2010 at 8:29 PM, Thiago Farina<tfransosi@...il.com>  wrote:
>>>
>>> On Sat, Dec 4, 2010 at 1:19 AM,<bookjovi@...il.com>  wrote:
>>>> fix error handling path
>>>>
>>>> Signed-off-by: Jovi Zhang<bookjovi@...il.com>
>>>>   kernel/perf_event.c |    2 --
>>>>   1 files changed, 0 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
>>>> index cb6c0d2..62f9e9d 100644
>>>> --- a/kernel/perf_event.c
>>>> +++ b/kernel/perf_event.c
>>>> @@ -1918,8 +1918,6 @@ static int get_callchain_buffers(void)
>>>>         }
>>>>
>>>>         err = alloc_callchain_buffers();
>>>> -       if (err)
>>>> -               release_callchain_buffers();
>>>
>>> Care to explain in the change log message? As I reader, is not clear
>>> to me what is wrong with this.
>>
>> Sorry, the description should be as:
>> fix error handling path. alloc_callchain_buffers() can return -ENOMEM,
>> in this time callchain_cpus_entries maybe is NULL, It will oops if
>> invoke release_callchain_buffers() when callchain_cpus_entries is
>> NULL.
>>
> I hope my understanding is right, is it?

One possible problem here is what if it returns an error other than 
-ENOMEM, and the buffers do need to be released?  Maybe you could change 
the code to

err = alloc_callchain_buffers();
if (err != -ENOMEM)
	release_callchain_buffers();


Currently, alloc_callchain_buffers cannot return any error code other 
than -ENOMEM, but that might change in the future.

- Corey
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