netdev - Re: [PATCH net] net: Use NAPI_* in test

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Message-ID: <20250912192749.GG224143@horms.kernel.org>
Date: Fri, 12 Sep 2025 20:27:49 +0100
From: Simon Horman <horms@...nel.org>
To: Samiullah Khawaja <skhawaja@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>,
	"David S . Miller " <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	willemb@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] net: Use NAPI_* in test_bit when stopping napi
 kthread

On Fri, Sep 12, 2025 at 08:26:03PM +0100, Simon Horman wrote:
> On Wed, Sep 10, 2025 at 08:37:16PM +0000, Samiullah Khawaja wrote:
> > napi_stop_kthread waits for the NAPI_STATE_SCHED_THREADED to be unset
> > before stopping the kthread. But it uses test_bit with the
> > NAPIF_STATE_SCHED_THREADED and that might stop the kthread early before
> > the flag is unset.
> > 
> > Use the NAPI_* variant of the NAPI state bits in test_bit instead.
> 
> I think it would be useful to mention the difference between 
> NAPI_STATE_SCHED_THREADED and NAPIF_STATE_SCHED_THREADED.
> 
> For me, that would be that one is a bit number, while
> the other is a mask with only the corresponding bit set.
> 
> > 
> > Tested:
> >  ./tools/testing/selftests/net/nl_netdev.py
> >  TAP version 13
> >  1..7
> >  ok 1 nl_netdev.empty_check
> >  ok 2 nl_netdev.lo_check
> >  ok 3 nl_netdev.page_pool_check
> >  ok 4 nl_netdev.napi_list_check
> >  ok 5 nl_netdev.dev_set_threaded
> >  ok 6 nl_netdev.napi_set_threaded
> >  ok 7 nl_netdev.nsim_rxq_reset_down
> >  # Totals: pass:7 fail:0 xfail:0 xpass:0 skip:0 error:0
> > 
> >  ./tools/testing/selftests/drivers/net/napi_threaded.py
> >  TAP version 13
> >  1..2
> >  ok 1 napi_threaded.change_num_queues
> >  ok 2 napi_threaded.enable_dev_threaded_disable_napi_threaded
> >  # Totals: pass:2 fail:0 xfail:0 xpass:0 skip:0 error:0
> > 
> > Fixes: 689883de94dd ("net: stop napi kthreads when THREADED napi is disabled")
> > Signed-off-by: Samiullah Khawaja <skhawaja@...gle.com>
> 
> With the above addressed, feel free to add:
> 
> Reviewed-by: Simon Horman <horms@...nel.org>
> 
> ...

I now see that this patch is present in net as
commit 247981eecd3d ("net: Use NAPI_* in test_bit when stopping napi kthread")

So I think we can safely ignore the comments in my previous email.