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

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Date: Thu, 13 Jul 2023 10:11:02 +0000
From: Dragos Tatulea <dtatulea@...dia.com>
To: Tariq Toukan <tariqt@...dia.com>, "ttoukan.linux@...il.com"
	<ttoukan.linux@...il.com>, "jbrouer@...hat.com" <jbrouer@...hat.com>, Saeed
 Mahameed <saeedm@...dia.com>, "saeed@...nel.org" <saeed@...nel.org>,
	"linyunsheng@...wei.com" <linyunsheng@...wei.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
CC: "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>, "brouer@...hat.com"
	<brouer@...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>
Subject: Re: mlx5 XDP redirect leaking memory on kernel 6.3

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...

Thanks,
Dragos

> 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
> > 
> > 
>