linux-kernel - Re: [RFC PATCH 1/6] Revert "PCI: Fix is_added/is

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Message-ID: <20180819022440.GG128050@bhelgaas-glaptop.roam.corp.google.com>
Date:   Sat, 18 Aug 2018 21:24:40 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     linux-pci@...r.kernel.org, Hari Vyas <hari.vyas@...adcom.com>,
        Ray Jui <ray.jui@...adcom.com>,
        Srinath Mannam <srinath.mannam@...adcom.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Jens Axboe <axboe@...nel.dk>, Lukas Wunner <lukas@...ner.de>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Marta Rybczynska <mrybczyn@...ray.eu>,
        Pierre-Yves Kerbrat <pkerbrat@...ray.eu>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/6] Revert "PCI: Fix is_added/is_busmaster race
 condition"

On Sat, Aug 18, 2018 at 01:24:51PM +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2018-08-17 at 10:44 -0500, Bjorn Helgaas wrote:
> > On Fri, Aug 17, 2018 at 02:48:57PM +1000, Benjamin Herrenschmidt wrote:
> > > This reverts commit 44bda4b7d26e9fffed6d7152d98a2e9edaeb2a76.
> > 
> > Just to be clear, if I understand correctly, this is a pure revert of
> > 44bda4b7d26e and as such it reintroduces the problem solved by that
> > commit.
> > 
> > If your solution turns out to be better, that's great, but it would be
> > nice to avoid the bisection hole of reintroducing the problem, then
> > fixing it again later.
> 
> There is no way to do that other than merging the revert and the fix
> into one. That said, the race is sufficiently hard to hit that I
> wouldn't worry too much about it.

OK, then at least mention that in the changelog.

> > > The new pci state mutex provides a simpler way of addressing
> > > this race and avoids the relative includes added to the powerpc
> > > code.
>