netdev - Re: [PATCH v4 bpf 2/2] selftests/bpf: extend map-in-map selftest to detect memory leaks

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Message-ID: <e0741aae-64fd-dd2c-d91d-d8eb0b79ba20@iogearbox.net>
Date:   Wed, 29 Jul 2020 23:17:09 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Jakub Sitnicki <jakub@...udflare.com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Kernel Team <kernel-team@...com>,
        Song Liu <songliubraving@...com>,
        linux- stable <stable@...r.kernel.org>
Subject: Re: [PATCH v4 bpf 2/2] selftests/bpf: extend map-in-map selftest to
 detect memory leaks

On 7/29/20 7:48 PM, Andrii Nakryiko wrote:
> On Wed, Jul 29, 2020 at 7:29 AM Jakub Sitnicki <jakub@...udflare.com> wrote:
>>
>> On Wed, Jul 29, 2020 at 06:09 AM CEST, Andrii Nakryiko wrote:
>>> Add test validating that all inner maps are released properly after skeleton
>>> is destroyed. To ensure determinism, trigger kernel-side synchronize_rcu()
>>> before checking map existence by their IDs.
>>>
>>> Acked-by: Song Liu <songliubraving@...com>
>>> Signed-off-by: Andrii Nakryiko <andriin@...com>
[...]
>>> +/*
>>> + * Trigger synchronize_cpu() in kernel.
>>
>> Nit: synchronize_*r*cu().
> 
> welp, yeah
> 
>>
>>> + *
>>> + * ARRAY_OF_MAPS/HASH_OF_MAPS lookup/update operations trigger
>>> + * synchronize_rcu(), if looking up/updating non-NULL element. Use this fact
>>> + * to trigger synchronize_cpu(): create map-in-map, create a trivial ARRAY
>>> + * map, update map-in-map with ARRAY inner map. Then cleanup. At the end, at
>>> + * least one synchronize_rcu() would be called.
>>> + */
>>
>> That's a cool trick. I'm a bit confused by "looking up/updating non-NULL
>> element". It looks like you're updating an element that is NULL/unset in
>> the code below. What am I missing?
> 
> I was basically trying to say that it has to be a successful lookup or
> update. For lookup that means looking up non-NULL (existing) entry.
> For update -- setting valid inner map FD.
> 
> Not sure fixing this and typo above is worth it to post v5.

Nope, I'll fix it up while applying.