linux-kernel - Re: [PATCH net-next] ppp: enable TX scatter-gather

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Message-ID: <20250917141434.596f6b8b@kernel.org>
Date: Wed, 17 Sep 2025 14:14:34 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Qingfang Deng <dqfext@...il.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, linux-ppp@...r.kernel.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, Felix Fietkau <nbd@....name>
Subject: Re: [PATCH net-next] ppp: enable TX scatter-gather

On Wed, 17 Sep 2025 19:00:16 +0800 Qingfang Deng wrote:
> On Tue, Sep 16, 2025 at 10:57 PM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Tue, 16 Sep 2025 10:57:49 +0800 Qingfang Deng wrote:  
> > > Can I modify dev->features directly under the spin lock (without
> > > .ndo_fix_features) ?  
> >
> > Hm, I'm not aware of a reason not to. You definitely need to hold
> > rtnl_lock, and call netdev_update_features() after.  
> 
> Will the modification race against __netdev_update_features(), where
> dev->features is assigned a new value?

Shouldn't race if we're holding rtnl_lock when we make the modification
and until we call netdev_update_features()? I'm just spitballing tho,
haven't studied the code.