Re: [PATCH] perf header: Fix lock/unlock imbalances

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 4/8/19 3:00 PM, Arnaldo Carvalho de Melo wrote:
> Em Mon, Apr 08, 2019 at 02:52:52PM -0500, Gustavo A. R. Silva escreveu:
>>
>>
>> On 4/8/19 2:35 PM, Arnaldo Carvalho de Melo wrote:
>>> Em Mon, Apr 08, 2019 at 01:26:09PM -0500, Gustavo A. R. Silva escreveu:
>>>>
>>>>
>>>> On 4/8/19 1:22 PM, Song Liu wrote:
>>>>>
>>>>>
>>>>>> On Apr 8, 2019, at 10:33 AM, Gustavo A. R. Silva <gustavo@embeddedor.com> wrote:
>>>>>>
>>>>>> Fix lock/unlock imbalances by refactoring the code a bit and adding
>>>>>> calls to up_write() before return.
>>>>>>
>>>>>> Addresses-Coverity-ID: 1444315 ("Missing unlock")
>>>>>> Addresses-Coverity-ID: 1444316 ("Missing unlock")
>>>>>> Fixes: a70a1123174a ("perf bpf: Save BTF information as headers to perf.data")
>>>>>> Fixes: 606f972b1361 ("perf bpf: Save bpf_prog_info information as headers to perf.data")
>>>>>> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
>>>>>
>>>>> Acked-by: Song Liu <songliubraving@fb.com>
>>>>>
>>>>> Thanks for the fix!
>>>>>
>>>>
>>>> Glad to help. :)
>>>
>>> Super cool, using the same idiom as the kernel and living in the kernel
>>> sources has its advantages 8-)
>>>
>>
>> :P
>>
>>> But see below, 
>>>
>>>>>> +++ b/tools/perf/util/header.c
>>>>>> @@ -2606,6 +2606,7 @@ static int process_bpf_prog_info(struct feat_fd *ff, void *data __maybe_unused)
>>>>>> 		perf_env__insert_bpf_prog_info(env, info_node);
>>>>>> 	}
>>>>>>
>>>>>> +	up_write(&env->bpf_progs.lock);
>>>>>> 	return 0;
>>>>>> out:
>>>>>> 	free(info_linear);
>>>>>> @@ -2623,7 +2624,9 @@ static int process_bpf_prog_info(struct feat_fd *ff __maybe_unused, void *data _
>>>>>> static int process_bpf_btf(struct feat_fd *ff, void *data __maybe_unused)
>>>>>> {
>>>>>> 	struct perf_env *env = &ff->ph->env;
>>>>>> +	struct btf_node *node;
>>>>>> 	u32 count, i;
>>>>>> +	int err = -1;
>>>
>>> Why are you using this 'err' variable? It is only set here and at the
>>> end, i.e. one write, one read. We could as well have that out: block
>>> return -1 straight away.
>>>
>>> Else we could do, see below
>>>
>>>>>>
>>>>>> 	if (ff->ph->needs_swap) {
>>>>>> 		pr_warning("interpreting btf from systems with endianity is not yet supported\n");
>>>>>> @@ -2636,31 +2639,33 @@ static int process_bpf_btf(struct feat_fd *ff, void *data __maybe_unused)
>>>>>> 	down_write(&env->bpf_progs.lock);
>>>>>>
>>>>>> 	for (i = 0; i < count; ++i) {
>>>>>> -		struct btf_node *node;
>>>>>> 		u32 id, data_size;
>>>>>>
>>>>>> +		node = NULL;
>>>>>> 		if (do_read_u32(ff, &id))
>>>>>> -			return -1;
>>>>>> +			goto out;
>>>>>> 		if (do_read_u32(ff, &data_size))
>>>>>> -			return -1;
>>>>>> +			goto out;
>>>>>>
>>>>>> 		node = malloc(sizeof(struct btf_node) + data_size);
>>>>>> 		if (!node)
>>>>>> -			return -1;
>>>>>> +			goto out;
>>>>>>
>>>>>> 		node->id = id;
>>>>>> 		node->data_size = data_size;
>>>>>>
>>>>>> -		if (__do_read(ff, node->data, data_size)) {
>>>>>> -			free(node);
>>>>>> -			return -1;
>>>>>> -		}
>>>>>> +		if (__do_read(ff, node->data, data_size))
>>>>>> +			goto out;
>>>>>>
>>>>>> 		perf_env__insert_btf(env, node);
>>>>>> 	}
>>>
>>>       err = 0;
>>>
>>>>>>
>>>
>>> out:
>>>
>>>>>> 	up_write(&env->bpf_progs.lock);
>>>
>>>       return err;
>>>
>>> And delete the rest.
>>>
>>> but I see, you used the same pattern in the first #ifdef HAVE_LIBBPF_SUPPORT
>>> block :-)
>>>
>>> Anyway, since we're fixing up that other case, we might as well
>>> streamline this, please check the patch below.
>>>
>>
>> Yeah. This is exactly how I would have coded this from the beginning. But, as you
>> correctly pointed out, I'm using the same pattern as in HAVE_LIBBPF_SUPPORT. :)
>>
>> Just a comment below...
>>
>>>>>> 	return 0;
>>>
>>>>>> +out:
>>>>>> +	up_write(&env->bpf_progs.lock);
>>>>>> +	free(node);
>>>>>> +	return err;
>>>
>>> So, that is what I'm applying, please holler if I introduced some
>>> problem:
>>>
>>> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
>>> index b9e693825873..2d2af2ac2b1e 100644
>>> --- a/tools/perf/util/header.c
>>> +++ b/tools/perf/util/header.c
>>> @@ -2606,6 +2606,7 @@ static int process_bpf_prog_info(struct feat_fd *ff, void *data __maybe_unused)
>>>  		perf_env__insert_bpf_prog_info(env, info_node);
>>>  	}
>>>  
>>> +	up_write(&env->bpf_progs.lock);
>>>  	return 0;
>>>  out:
>>>  	free(info_linear);
>>> @@ -2623,7 +2624,9 @@ static int process_bpf_prog_info(struct feat_fd *ff __maybe_unused, void *data _
>>>  static int process_bpf_btf(struct feat_fd *ff, void *data __maybe_unused)
>>>  {
>>>  	struct perf_env *env = &ff->ph->env;
>>> +	struct btf_node *node = NULL;
>>>  	u32 count, i;
>>> +	int err = -1;
>>>  
>>>  	if (ff->ph->needs_swap) {
>>>  		pr_warning("interpreting btf from systems with endianity is not yet supported\n");
>>> @@ -2636,31 +2639,32 @@ static int process_bpf_btf(struct feat_fd *ff, void *data __maybe_unused)
>>>  	down_write(&env->bpf_progs.lock);
>>>  
>>>  	for (i = 0; i < count; ++i) {
>>> -		struct btf_node *node;
>>>  		u32 id, data_size;
>>>  
>>>  		if (do_read_u32(ff, &id))
>>> -			return -1;
>>> +			goto out;
>>>  		if (do_read_u32(ff, &data_size))
>>> -			return -1;
>>> +			goto out;
>>>  
>>>  		node = malloc(sizeof(struct btf_node) + data_size);
>>>  		if (!node)
>>> -			return -1;
>>> +			goto out;
>>>  
>>>  		node->id = id;
>>>  		node->data_size = data_size;
>>>  
>>> -		if (__do_read(ff, node->data, data_size)) {
>>> -			free(node);
>>> -			return -1;
>>> -		}
>>> +		if (__do_read(ff, node->data, data_size))
>>> +			goto out;
>>>  
>>>  		perf_env__insert_btf(env, node);
>>> +		node = NULL;
>>
>> If we move this assignment to the beginning of the for loop, as in
>> the original patch, we avoid the same assignment while declaring
>> node at the beginning of the function.
> 
> No, we don't, since the common exit path frees node, we better not free
> the last node in the success case, that is why I moved it to the end,
> i.e. after we're done with it, nullify it, so that the last btf_node
> isn't freed in the now uncoditionall free(node); call :-)
> 

Yep. You're right.

So, everything is fine now. :)

Thanks
--
Gustavo