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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Tue, 23 Mar 2021 07:51:09 +0100
Message-ID: <CACT4Y+bNsEU3ZbHioBvZ9xbbML3TtX8f4WkyHLGv9OT4go1e9g@mail.gmail.com>
Subject: Re: [PATCH] net: make unregister netdev warning timeout configurable
To:     David Miller <davem@davemloft.net>
Cc:     Eric Dumazet <edumazet@google.com>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Mon, Mar 22, 2021 at 8:26 PM David Miller <davem@davemloft.net> wrote:
>
> From: Dmitry Vyukov <dvyukov@google.com>
> Date: Sat, 20 Mar 2021 15:28:51 +0100
>
> > netdev_wait_allrefs() issues a warning if refcount does not drop to 0
> > after 10 seconds. While 10 second wait generally should not happen
> > under normal workload in normal environment, it seems to fire falsely
> > very often during fuzzing and/or in qemu emulation (~10x slower).
> > At least it's not possible to understand if it's really a false
> > positive or not. Automated testing generally bumps all timeouts
> > to very high values to avoid flake failures.
> > Make the timeout configurable for automated testing systems.
> > Lowering the timeout may also be useful for e.g. manual bisection.
> > The default value matches the current behavior.
> >
> > Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
> > Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=211877
> > Cc: netdev@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
>
> I'd say a sysctl knob is much better than a compile time setting for this.
> That way stock kernels can be used in these testing scenerios.

FTR, I've mailed v2 with a sysctl:
https://lore.kernel.org/netdev/20210323064923.2098711-1-dvyukov@google.com/T/#u