linux-kernel - Re: [PATCH bpf-next v3 03/14] selftests/bpf: test

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Message-ID: <9c96720e-091c-434e-9060-c47ea59ad91e@bootlin.com>
Date: Thu, 18 Sep 2025 10:07:47 +0200
From: Bastien Curutchet <bastien.curutchet@...tlin.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc: Björn Töpel <bjorn@...nel.org>,
 Magnus Karlsson <magnus.karlsson@...el.com>,
 Jonathan Lemon <jonathan.lemon@...il.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>,
 Shuah Khan <shuah@...nel.org>, "David S. Miller" <davem@...emloft.net>,
 Jakub Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 Alexis Lothore <alexis.lothore@...tlin.com>, netdev@...r.kernel.org,
 bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 03/14] selftests/bpf: test_xsk: Fix memory
 leaks

On 9/17/25 8:33 PM, Maciej Fijalkowski wrote:
> On Wed, Sep 17, 2025 at 05:32:55PM +0200, Bastien Curutchet wrote:
>> Hi Maciej
>>
>> On 9/16/25 7:58 PM, Maciej Fijalkowski wrote:
>>> On Thu, Sep 04, 2025 at 12:10:18PM +0200, Bastien Curutchet (eBPF Foundation) wrote:
>>>> Some tests introduce memory leaks by not freeing all the pkt_stream
>>>> objects they're creating.
>>>>
>>>> Fix these memory leaks.
>>>
>>> I would appreciate being more explicit here as I've been scratching my
>>> head here.
>>>
>>
>> Indeed it lacks details sorry. IIRC I spotted these with valgrind, maybe I
>> can add valgrind's output to the commit log in next iteration.
>>
>>>   From what I see the problem is with testapp_stats_rx_dropped() as it's the
>>> one case that uses replace and receive half of pkt streams, both of which
>>> overwrite the default pkt stream. So we lose a pointer to one of pkt
>>> streams and leak it eventually.
>>>
>>
>> Exactly, we lose pointers in some cases when xsk->pkt_stream gets replaced
>> by a new stream. testapp_stats_rx_dropped() is the most convoluted of these
>> cases.
> 
> pkt_stream_restore_default() is supposed to delete overwritten pkt_stream
> and set ::pkt_stream to default one, explicit pkt_stream_delete() in bunch
> of tests is redundant IMHO.
> 
> Per my understanding testapp_stats_rx_dropped() and
> testapp_xdp_shared_umem() need fixing. First generate pkt_stream twice and
> second generates pkt_stream on each xsk from xsk_arr, where normally
> xsk_arr[0] gets pkt_streams and xsk_arr[1] have them NULLed.
> 

I took another look at it, and I agree with you: the pkt_stream_delete() 
calls I added in testapp_stats_rx_full() and testapp_stats_fill_empty() 
don't seem necessary.
It still feels a bit strange to overwrite a pointer without freeing it 
right away, but I don't have a strong opinion on this. I'm fine with 
only fixing testapp_stats_rx_dropped() and testapp_xdp_shared_umem() in 
the next iteration.

Best regards,
-- 
Bastien Curutchet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com