linux-kernel - Re: [PATCH net-next] page_pool: add debug for release to cache from wrong CPU

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ztotepnqvbyzwtmqox5433lp6wix6jzj6tf3zkagwvfzf33trz@khcwhwwg7gxx>
Date: Tue, 23 Sep 2025 16:00:27 +0000
From: Dragos Tatulea <dtatulea@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Jesper Dangaard Brouer <hawk@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Ilias Apalodimas <ilias.apalodimas@...aro.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Clark Williams <clrkwllms@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, netdev@...r.kernel.org, 
	Tariq Toukan <tariqt@...dia.com>, linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH net-next] page_pool: add debug for release to cache from
 wrong CPU

On Tue, Sep 23, 2025 at 08:34:39AM -0700, Jakub Kicinski wrote:
> On Tue, 23 Sep 2025 15:23:02 +0000 Dragos Tatulea wrote:
> > On Mon, Sep 22, 2025 at 04:18:27PM -0700, Jakub Kicinski wrote:
> > > On Sat, 20 Sep 2025 09:25:31 +0000 Dragos Tatulea wrote:  
> > > > The point is not to chase leaks but races from doing a recycle to cache
> > > > from the wrong CPU. This is how XDP issue was caught where
> > > > xdp_set_return_frame_no_direct() was not set appropriately for cpumap [1].
> > > > 
> > > > My first approach was to __page_pool_put_page() but then I figured that
> > > > the warning should live closer to where the actual assignment happens.
> > > > 
> > > > [1] https://lore.kernel.org/all/e60404e2-4782-409f-8596-ae21ce7272c4@kernel.org/  
> > > 
> > > Ah, that thing. I wonder whether the complexity in the driver-facing 
> > > xdp_return API is really worth the gain here. IIUC we want to extract
> > > the cases where we're doing local recycling and let those cases use
> > > the lockless cache. But all those cases should be caught by automatic
> > > local recycling detection, so caller can just pass false..
> > >  
> > This patch was simply adding the debugging code to catch the potential
> > misuse from any callers.
> > 
> > I was planning to send another patch for the xdp_return() API part
> > once/if this one got accepted. If it makes more sense I can bundle them
> > together in a RFC (as merge window is coming).
> 
> Combined RFC would make sense, yes.
>
Ack.

> But you get what I'm saying right? I'm questioning whether _rx_napi()
> flavor of calls even make sense these days. If they don't I'd think
> the drivers can't be wrong and the need for the debug check is
> diminished?
I got the point for XDP. I am not sure if you are arguing the same thing
for the other users though. For example. there are many drivers
releasing netmems with direct=true.

Thanks,
Dragos