linux-kernel - Re: netconsole warning in 4.19.0-rc7

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Message-ID: <CAM_iQpWJfMWRY1TZRDz+GgjGJj_ySjmb42hjPyAtcakzWqnLeg@mail.gmail.com>
Date:   Tue, 16 Oct 2018 22:16:57 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Dave Jones <davej@...emonkey.org.uk>, Meelis Roos <mroos@...ux.ee>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: netconsole warning in 4.19.0-rc7

On Tue, Oct 16, 2018 at 8:50 PM Dave Jones <davej@...emonkey.org.uk> wrote:
>
> On Tue, Oct 16, 2018 at 11:40:47PM -0400, Dave Jones wrote:
>
>  >  > This is exactly what I mentioned in my review here:
>  >  > https://marc.info/?l=linux-netdev&m=153816136624679&w=2
>  >  >
>  >  > "But irq is disabled here, so not sure if rcu_read_lock_bh()
>  >  > could cause trouble... "
>  >
>  > Not sure why this didn't show up for me when I was developing that
>  > patch, but I can now reproduce this.  The patch below fixes it for
>  > me, but I'm not sure if there are still any side-effects.
>  > There's also a missed unlock in the error path.
>
> I took another look at that error path. Turns out this is all we need I
> think..

Double check if rcu_dereference_bh() is happy with it.

Don't trust me, enable the relevant Kconfig and trust your test. ;)