netdev - Re: [PATCH v3 perf,bpf 05/11] perf, bpf: save bpf_prog_info in a rbtree in perf

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Message-ID: <55885497-4542-4FED-97E0-64664059FFC3@fb.com>
Date:   Tue, 19 Feb 2019 14:21:03 +0000
From:   Song Liu <songliubraving@...com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     Netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "acme@...hat.com" <acme@...hat.com>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "namhyung@...nel.org" <namhyung@...nel.org>
Subject: Re: [PATCH v3 perf,bpf 05/11] perf, bpf: save bpf_prog_info in a
 rbtree in perf_env



> On Feb 19, 2019, at 12:51 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> 
> On Tue, Feb 19, 2019 at 05:52:20AM +0000, Song Liu wrote:
>> 
>> 
>>> On Feb 17, 2019, at 3:05 PM, Jiri Olsa <jolsa@...hat.com> wrote:
>>> 
>>> On Fri, Feb 15, 2019 at 01:53:48PM -0800, Song Liu wrote:
>>> 
>>> SNIP
>>> 
>>>> 	info_linear = bpf_program__get_prog_info_linear(fd, arrays);
>>>> 	if (IS_ERR_OR_NULL(info_linear)) {
>>>> @@ -151,8 +165,8 @@ static int perf_event__synthesize_one_bpf_prog(struct perf_tool *tool,
>>>> 						     machine, process);
>>>> 	}
>>>> 
>>>> -	/* Synthesize PERF_RECORD_BPF_EVENT */
>>>> 	if (opts->bpf_event) {
>>>> +		/* Synthesize PERF_RECORD_BPF_EVENT */
>>>> 		*bpf_event = (struct bpf_event){
>>>> 			.header = {
>>>> 				.type = PERF_RECORD_BPF_EVENT,
>>>> @@ -165,6 +179,19 @@ static int perf_event__synthesize_one_bpf_prog(struct perf_tool *tool,
>>>> 		memcpy(bpf_event->tag, info->tag, BPF_TAG_SIZE);
>>>> 		memset((void *)event + event->header.size, 0, machine->id_hdr_size);
>>>> 		event->header.size += machine->id_hdr_size;
>>>> +
>>>> +		/* save bpf_prog_info to env */
>>>> +		info_node = malloc(sizeof(struct bpf_prog_info_node));
>>>> +		if (info_node) {
>>>> +			info_node->info_linear = info_linear;
>>>> +			perf_env__insert_bpf_prog_info(env, info_node);
>>>> +			info_linear = NULL;
>>>> +		}
>>> 
>>> what if the allocation fails? we don't care?
>>> 
>>> jirka
>> 
>> My original plan is to just ignore it and accept that this program
>> doesn't have annotation. Any suggestion on what would be a better 
>> approach?
> 
> there's an error path in the function, I'd bail out if the malloc fails
> 
> jirka

If we go to bail out here, we will skip processing PERF_RECORD_BPF_EVENT. 
When malloc fails, this is still valuable information that we should try 
to save. So I think we don't have to bail out here. I will add a comment
to explain this. 

Thanks,
Song