Re: [PATCH net] net: devmem: use READ_ONCE/WRITE_ONCE on binding->dev

[Mina Almasry]

On Wed, Feb 25, 2026 at 7:14 AM Bobby Eshleman <bobbyeshleman@xxxxxxxxx> wrote:
>
> On Tue, Feb 24, 2026 at 05:49:42PM -0800, Stanislav Fomichev wrote:
> > On 02/23, Bobby Eshleman wrote:
> > > From: Bobby Eshleman <bobbyeshleman@xxxxxxxx>
> > >
> > > binding->dev is protected on the write-side in
> > > mp_dmabuf_devmem_uninstall() against concurrent writes, but due to the
> > > concurrent bare read in net_devmem_get_binding() it should be wrapped in
> > > a READ_ONCE/WRITE_ONCE pair to make sure no compiler optimizations play
> > > with the underlying register in unforeseen ways.
> > >
> > > Fixes: bd61848900bf ("net: devmem: Implement TX path")
> > > Signed-off-by: Bobby Eshleman <bobbyeshleman@xxxxxxxx>

Looks correct to me, and AFAIU Stan is right, we might as well
annotate all the reads of ->dev as technically there could be a dmabuf
uninstall happing concurrently on another CPU. I also think it's
probably good to annotate potential races.

The ->dev write in dmabuf binding doesn't need WRITE_ONCE annotation I
guess because it's initialization, it can't race with any reads.

This makes me wonder what other fields in dmabuf need annotations. I
hope I didn't miss many more.

I would add this is really not a critical bug because
net_devmem_get_binding() is in TX path, and it is more than fine here
if we fail this check if there is an unbind happening in paraller with
sendmsg(), but it's probably good to annotate potential races anyway.

-- 
Thanks,
Mina