linux-kernel - Re: [PATCH net] net: dev: Detect dev_hold() after netdev_wait

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Message-ID: <CAG48ez0WY2WgPjk4zuT5tZdEy_qt+fh+R_XTr21_Vug9a8ggmg@mail.gmail.com>
Date:   Fri, 28 Jan 2022 04:00:34 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Oliver Neukum <oneukum@...e.com>
Subject: Re: [PATCH net] net: dev: Detect dev_hold() after netdev_wait_allrefs()

On Fri, Jan 28, 2022 at 3:53 AM Eric Dumazet <edumazet@...gle.com> wrote:
> On Thu, Jan 27, 2022 at 6:48 PM Jann Horn <jannh@...gle.com> wrote:
>
> > When someone is using NET_DEV_REFCNT_TRACKER for slow debugging, they
> > should also be able to take the performance hit of
> > CONFIG_PCPU_DEV_REFCNT and rely on the normal increment-from-zero
> > detection of the generic refcount code, right? (Maybe
> > NET_DEV_REFCNT_TRACKER should depend on !CONFIG_PCPU_DEV_REFCNT?)
>
> NET_DEV_REFCNT_TRACKER is not slow, I think it has neglectable cost really.
> (I could not see any difference in my tests)

Ah, sorry. I misread the Kconfig text.