linux-kernel - Re: [PATCH v2 0/9] deferred_probe

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Message-ID: <CAMuHMdXQCwMQj_ZiOBAzusdCxd8w6NbTqD_7nzykhVs+UWx8Gw@mail.gmail.com>
Date:   Wed, 8 Jun 2022 20:47:36 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        David Ahern <dsahern@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        netdev <netdev@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
Subject: Re: [PATCH v2 0/9] deferred_probe_timeout logic clean up

Hi Saravana,

On Wed, Jun 8, 2022 at 8:13 PM Saravana Kannan <saravanak@...gle.com> wrote:
> On Wed, Jun 8, 2022 at 3:26 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Wed, Jun 8, 2022 at 6:17 AM Saravana Kannan <saravanak@...gle.com> wrote:
> > > On Tue, Jun 7, 2022 at 5:55 PM Saravana Kannan <saravanak@...gle.com> wrote:
> > > > On Tue, Jun 7, 2022 at 11:13 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > > > On Wed, Jun 1, 2022 at 12:46 PM Saravana Kannan <saravanak@...gle.com> wrote:
> > > > > > This series is based on linux-next + these 2 small patches applies on top:
> > > > > > https://lore.kernel.org/lkml/20220526034609.480766-1-saravanak@google.com/
> > > > > >
> > > > > > A lot of the deferred_probe_timeout logic is redundant with
> > > > > > fw_devlink=on.  Also, enabling deferred_probe_timeout by default breaks
> > > > > > a few cases.
> > > > > >
> > > > > > This series tries to delete the redundant logic, simplify the frameworks
> > > > > > that use driver_deferred_probe_check_state(), enable
> > > > > > deferred_probe_timeout=10 by default, and fixes the nfsroot failure
> > > > > > case.
> > > > > >
> > > > > > The overall idea of this series is to replace the global behavior of
> > > > > > driver_deferred_probe_check_state() where all devices give up waiting on
> > > > > > supplier at the same time with a more granular behavior:
> > > > > >
> > > > > > 1. Devices with all their suppliers successfully probed by late_initcall
> > > > > >    probe as usual and avoid unnecessary deferred probe attempts.
> > > > > >
> > > > > > 2. At or after late_initcall, in cases where boot would break because of
> > > > > >    fw_devlink=on being strict about the ordering, we
> > > > > >
> > > > > >    a. Temporarily relax the enforcement to probe any unprobed devices
> > > > > >       that can probe successfully in the current state of the system.
> > > > > >       For example, when we boot with a NFS rootfs and no network device
> > > > > >       has probed.
> > > > > >    b. Go back to enforcing the ordering for any devices that haven't
> > > > > >       probed.
> > > > > >
> > > > > > 3. After deferred probe timeout expires, we permanently give up waiting
> > > > > >    on supplier devices without drivers. At this point, whatever devices
> > > > > >    can probe without some of their optional suppliers end up probing.
> > > > > >
> > > > > > In the case where module support is disabled, it's fairly
> > > > > > straightforward and all device probes are completed before the initcalls
> > > > > > are done.
> > > > > >
> > > > > > Patches 1 to 3 are fairly straightforward and can probably be applied
> > > > > > right away.
> > > > > >
> > > > > > Patches 4 to 6 are for fixing the NFS rootfs issue and setting the
> > > > > > default deferred_probe_timeout back to 10 seconds when modules are
> > > > > > enabled.
> > > > > >
> > > > > > Patches 7 to 9 are further clean up of the deferred_probe_timeout logic
> > > > > > so that no framework has to know/care about deferred_probe_timeout.
> > > > > >
> > > > > > Yoshihiro/Geert,
> > > > > >
> > > > > > If you can test this patch series and confirm that the NFS root case
> > > > > > works, I'd really appreciate that.
> > > > >
> > > > > Thanks, I gave this a try on various boards I have access to.
> > > > > The results were quite positive. E.g. the compile error I saw on v1
> > > > > (implicit declation of fw_devlink_unblock_may_probe(), which is no longer
> > > > >  used in v2) is gone.
> > > >
> > > > Thanks a lot for testing these.
> > > >
> > > > > However, I'm seeing a weird error when userspace (Debian9 nfsroot) is
> > > > > starting:

> > Setting fw_devlink_strict to true vs. false seems to influence which of
> > two different failures will happen:
> >   - rcar-csi2: probe of feaa0000.csi2 failed with error -22
> >   - rcar-vin: probe of e6ef5000.video failed with error -22
> > The former causes the NULL pointer dereference later.
> > The latter existed before, but I hadn't noticed it, and bisection
> > led to the real culprit (commit 3e52419ec04f9769 ("media: rcar-{csi2,vin}:
> > Move to full Virtual Channel routing per CSI-2 IP").
>
> If you revert that patch, does this series work fine? If yes, are you
> happy with giving this a Tested-by?

Sure, sorry for forgetting that ;-)

Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds