netdev - Re: [PATCH bpf-next v4 1/2] bpf: extend stackmap to save binary_build

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Message-ID: <a7ac3a74-959f-af35-81ce-a8c05be29b68@fb.com>
Date:   Mon, 12 Mar 2018 14:31:46 -0700
From:   Alexei Starovoitov <ast@...com>
To:     Song Liu <songliubraving@...com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        Teng Qin <qinteng@...com>
Subject: Re: [PATCH bpf-next v4 1/2] bpf: extend stackmap to save
 binary_build_id+offset instead of address

On 3/12/18 2:12 PM, Song Liu wrote:
>
>> On Mar 12, 2018, at 2:00 PM, Alexei Starovoitov <ast@...com> wrote:
>>
>> On 3/12/18 1:39 PM, Song Liu wrote:
>>> +	page = find_get_page(vma->vm_file->f_mapping, 0);
>>
>> did you test it with config_debug_atomic_sleep ?
>> it should have complained...
>
> Yeah, I have CONFIG_DEBUG_ATOMIC_SLEEP=y.
>
> I think find_get_page() will not sleep. The variation find_get_page_flags()
> may sleep with flag FGP_CREAT.

I see. gfp_mask == 0 and no locks. should work indeed.
curious how perf report looks like for heavy bpf_get_stackid() usage?