netdev - Re: [BUG] mlx5_core memory management issue

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Message-ID: <aJuxY9oTtxSn4qZP@861G6M3>
Date: Tue, 12 Aug 2025 16:25:55 -0500
From: Chris Arges <carges@...udflare.com>
To: Dragos Tatulea <dtatulea@...dia.com>
Cc: Jesse Brandeburg <jbrandeburg@...udflare.com>, netdev@...r.kernel.org,
	bpf@...r.kernel.org, kernel-team <kernel-team@...udflare.com>,
	Jesper Dangaard Brouer <hawk@...nel.org>, tariqt@...dia.com,
	saeedm@...dia.com, Leon Romanovsky <leon@...nel.org>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	John Fastabend <john.fastabend@...il.com>,
	Simon Horman <horms@...nel.org>,
	Andrew Rzeznik <arzeznik@...udflare.com>,
	Yan Zhai <yan@...udflare.com>
Subject: Re: [BUG] mlx5_core memory management issue

On 2025-08-12 20:19:30, Dragos Tatulea wrote:
> On Tue, Aug 12, 2025 at 11:55:39AM -0700, Jesse Brandeburg wrote:
> > On 8/12/25 8:44 AM, 'Dragos Tatulea' via kernel-team wrote:
> > 
> > > diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> > > index 482d284a1553..484216c7454d 100644
> > > --- a/kernel/bpf/devmap.c
> > > +++ b/kernel/bpf/devmap.c
> > > @@ -408,8 +408,10 @@ static void bq_xmit_all(struct xdp_dev_bulk_queue *bq, u32 flags)
> > >          /* If not all frames have been transmitted, it is our
> > >           * responsibility to free them
> > >           */
> > > +       xdp_set_return_frame_no_direct();
> > >          for (i = sent; unlikely(i < to_send); i++)
> > >                  xdp_return_frame_rx_napi(bq->q[i]);
> > > +       xdp_clear_return_frame_no_direct();
> > 
> > Why can't this instead just be xdp_return_frame(bq->q[i]); with no
> > "no_direct" fussing?
> > 
> > Wouldn't this be the safest way for this function to call frame completion?
> > It seems like presuming the calling context is napi is wrong?
> >
> It would be better indeed. Thanks for removing my horse glasses!
> 
> Once Chris verifies that this works for him I can prepare a fix patch.
>
Working on that now, I'm testing a kernel with the following change:

---

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 3aa002a47..ef86d9e06 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -409,7 +409,7 @@ static void bq_xmit_all(struct xdp_dev_bulk_queue *bq, u32 flags)
         * responsibility to free them
         */
        for (i = sent; unlikely(i < to_send); i++)
-               xdp_return_frame_rx_napi(bq->q[i]);
+               xdp_return_frame(bq->q[i]);
 
 out:
        bq->count = 0;