netdev - Re: mlx5 XDP redirect leaking memory on kernel 6.3

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Date: Thu, 13 Jul 2023 16:58:04 +0200
From: Jesper Dangaard Brouer <jbrouer@...hat.com>
To: Dragos Tatulea <dtatulea@...dia.com>, Tariq Toukan <tariqt@...dia.com>,
 "jbrouer@...hat.com" <jbrouer@...hat.com>, Saeed Mahameed
 <saeedm@...dia.com>, "saeed@...nel.org" <saeed@...nel.org>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 Greg KH <gregkh@...uxfoundation.org>
Cc: brouer@...hat.com, "maxtram95@...il.com" <maxtram95@...il.com>,
 "lorenzo@...nel.org" <lorenzo@...nel.org>,
 "alexander.duyck@...il.com" <alexander.duyck@...il.com>,
 "kheib@...hat.com" <kheib@...hat.com>,
 "ilias.apalodimas@...aro.org" <ilias.apalodimas@...aro.org>,
 "mkabat@...hat.com" <mkabat@...hat.com>, "atzin@...hat.com"
 <atzin@...hat.com>, "fmaurer@...hat.com" <fmaurer@...hat.com>,
 "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
 "jbenc@...hat.com" <jbenc@...hat.com>,
 "linyunsheng@...wei.com" <linyunsheng@...wei.com>,
 "ttoukan.linux@...il.com" <ttoukan.linux@...il.com>
Subject: Re: mlx5 XDP redirect leaking memory on kernel 6.3



On 13/07/2023 12.11, Dragos Tatulea wrote:
> Gi Jesper,
> On Thu, 2023-07-13 at 11:20 +0200, Jesper Dangaard Brouer wrote:
>> Hi Dragos,
>>
>> Below you promised to work on a fix for XDP redirect memory leak...
>> What is the status?
>>
> The fix got merged into net a week ago:
> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/drivers/net/ethernet/mellanox/mlx5/core?id=7abd955a58fb0fcd4e756fa2065c03ae488fcfa7
> 
> Just forgot to follow up on this thread. Sorry about that...
> 

Good to see it being fixed in net.git commit:
  7abd955a58fb ("net/mlx5e: RX, Fix page_pool page fragment tracking for 
XDP")

This need to be backported into stable tree 6.3, but I can see 6.3.13 is 
marked EOL (End-of-Life).
Can we still get this fix applied? (Cc. GregKH)

--Jesper

> 
>> On 23/05/2023 18.35, Dragos Tatulea wrote:
>>>
>>> On Tue, 2023-05-23 at 17:55 +0200, Jesper Dangaard Brouer wrote:
>>>>
>>>> When the mlx5 driver runs an XDP program doing XDP_REDIRECT, then memory
>>>> is getting leaked. Other XDP actions, like XDP_DROP, XDP_PASS and XDP_TX
>>>> works correctly. I tested both redirecting back out same mlx5 device and
>>>> cpumap redirect (with XDP_PASS), which both cause leaking.
>>>>
>>>> After removing the XDP prog, which also cause the page_pool to be
>>>> released by mlx5, then the leaks are visible via the page_pool periodic
>>>> inflight reports. I have this bpftrace[1] tool that I also use to detect
>>>> the problem faster (not waiting 60 sec for a report).
>>>>
>>>>     [1]
>>>> https://github.com/xdp-project/xdp-project/blob/master/areas/mem/bpftrace/page_pool_track_shutdown01.bt
>>>>
>>>> I've been debugging and reading through the code for a couple of days,
>>>> but I've not found the root-cause, yet. I would appreciate new ideas
>>>> where to look and fresh eyes on the issue.
>>>>
>>>>
>>>> To Lin, it looks like mlx5 uses PP_FLAG_PAGE_FRAG, and my current
>>>> suspicion is that mlx5 driver doesn't fully release the bias count (hint
>>>> see MLX5E_PAGECNT_BIAS_MAX).
>>>>
>>>
>>> Thanks for the report Jesper. Incidentally I've just picked up this issue
>>> today
>>> as well.
>>>
>>> On XDP redirect and tx, the page is set to skip the bias counter release
>>> with
>>> the expectation that page_pool_put_defragged_page will be called from [1].
>>> But,
>>> as I found out now, during XDP redirect only one fragment of the page is
>>> released in xdp core [2]. This is where the leak is coming from.
>>>
>>> We'll provide a fix soon.
>>>
>>> [1]
>>> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c#n665
>>>
>>> [2]
>>> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/net/core/xdp.c#n390
>>>
>>> Thanks,
>>> Dragos
>>>
>>>
>>
>