linux-kernel - Re: [PATCH net] net: dlink: use dev_kfree_skb_any instead of dev_kfree

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Message-ID: <20251004095421.GC3060232@horms.kernel.org>
Date: Sat, 4 Oct 2025 10:54:21 +0100
From: Simon Horman <horms@...nel.org>
To: Yeounsu Moon <yyyynoom@...il.com>
Cc: 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>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: dlink: use dev_kfree_skb_any instead of
 dev_kfree_skb

On Fri, Oct 03, 2025 at 07:51:25PM +0900, Yeounsu Moon wrote:
> On Fri Oct 3, 2025 at 5:17 PM KST, Simon Horman wrote:
> > On Fri, Oct 03, 2025 at 11:23:00AM +0900, Yeounsu Moon wrote:
> >> Replace `dev_kfree_skb()` with `dev_kfree_skb_any()` in `start_xmit()`
> >> which can be called from hard irq context (netpoll) and from other
> >> contexts.
> >> 
> >> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> >> Signed-off-by: Yeounsu Moon <yyyynoom@...il.com>
> >> Tested-on: D-Link DGE-550T Rev-A3
> >
> > Hi,
> Hello, Simon!
> >
> > I am curious to know why this problem has come up now.
> This came up because I have the hardware and recently dug into the code.
> Until then, it was not considered an issue, because nobody raised it as
> such.
> > Or more to the point, why it has not come up since the cited commit
> > was made, 20 years ago.
> I think there are two combined reasons why it has not surfaced for two
> decades:
> 1. very few people actually had this device/driver in use.
> 2. The problem is difficult to reproduce: one must use `netpoll`, and at
> the same time the `link_speed` must drop to zero.
> >
> > I am also curious to know how the problem was found.
> > By inspection? Through testing? Other?
> While looking at the `dl2k.c` code, I noticed that its logic calls
> either `dev_kfree_skb()` or `dev_consume_skb_irq()` depending on
> interrupt context. That logic gave me the sense that a similar issue
> could exist elsewhere.
> >
> > ...
> And read other driver codes and commit messages, check `networking/netdevices`
> (.ndo_start_xmit), enable `netpoll` and set up  `netconsole`, read
> `net/core/netpoll.c`, read comment in `include/linux/netdevice.h`,
> add countless `printk()`s, build millions of times... and so on.

Hi Yeounsu,

Thanks for your detailed response.

I do think it would be useful to add something like this to the commit
message:

  Found by inspection.

But in any case, this patch looks good to me.

Reviewed-by: Simon Horman <horms@...nel.org>