Re: [PATCH net] netpoll: prevent hanging NAPI when netcons gets enabled

[Jakub Kicinski <kuba@kernel.org>]

On Fri, 25 Jul 2025 14:23:26 +0200 Paolo Abeni wrote:
> > If this warning hits the next virtio_close() will hang.
> > 
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Reported-by: Paolo Abeni <pabeni@redhat.com>
> > Link: https://lore.kernel.org/c5a93ed1-9abe-4880-a3bb-8d1678018b1d@redhat.com
> > Signed-off-by: Jakub Kicinski <kuba@kernel.org>  
> 
> It's not clear to me if you have been able to validate the patch into
> NIPA already?

Sorry for the omission, I sent the patch in the evening after just 
3 iterations but left the test running. It completed 30 iterations
cleanly (boot, run the selected tests, no hangs).

> > +static int netconsole_setup_and_enable(struct netconsole_target *nt)
> > +{
> > +	int ret;
> > +
> > +	ret = netpoll_setup(&nt->np);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* Make sure all NAPI polls which started before dev->npinfo
> > +	 * was visible have exited before we start calling NAPI poll.
> > +	 * NAPI skips locking if dev->npinfo is NULL.
> > +	 */
> > +	synchronize_rcu();  
> 
> I'm wondering if it would make any sense to move the above in
> netpoll_setup(), make the exposed symbol safe.

Fair, somehow I convinced myself that the nt->enabled = true;
is more relevant.