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Date: Mon, 4 May 2026 18:00:04 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Dragos Tatulea <dtatulea@nvidia.com>
Cc: =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>, "David S. Miller"
 <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, Paolo Abeni
 <pabeni@redhat.com>, Simon Horman <horms@kernel.org>, Daniel Borkmann
 <daniel@iogearbox.net>, Martin Karsten <mkarsten@uwaterloo.ca>, Gal
 Pressman <gal@nvidia.com>, Tariq Toukan <tariqt@nvidia.com>, Joe Damato
 <joe@dama.to>, Frederik Deweerdt <fdeweerdt@fastly.com>,
 netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH net-next 1/2] net: napi: Fix interrupts permanently
 disabled during busy poll
Message-ID: <20260504180004.7b9955eb@kernel.org>
In-Reply-To: <4onzzvtgdyj5k4himhtv4dsga4dnunk4ppjyqgam6us44biear@7vvozjz2ywrr>
References: <20260428175134.1197036-2-dtatulea@nvidia.com>
	<20260428175134.1197036-3-dtatulea@nvidia.com>
	<20260428173844.1354aabe@kernel.org>
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On Mon, 4 May 2026 11:30:47 +0000 Dragos Tatulea wrote:
> > > That would also follow the scheme in napi_schedule_done(). (Note that
> > > swapping arm/clear does mean that we can get a wasted-timer outcome.)
> > >  
> > If it is wasted is fine. I figured that this could end up with a timer
> > scheduled after the napi deletion:
> > 
> > 1. busy_poll_stop(): clears SCHED bit.
> > 2. napi_disable() runs past SCHED wait, cancels timer and caller
> >    deletes napi mem.
> > 3. busy_poll_stop(): napi->timer is armed but napi is freed memory
> >    by now.
> > 
> > What am I missing here?
> >  
> Gentle ping. Once I understand how/why the above is incorrect I can
> update the patch and send it.

Eh, I didn't respond cause I got depressed. Look around for the pattern
you are calling incorrect in existing code and you'll figure out why...