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    SubjectRe: [PATCH v1] driver core: Extend deferred probe timeout on driver registration
    On Fri, May 20, 2022 at 5:04 PM Nathan Chancellor <nathan@kernel.org> wrote:
    >
    > On Fri, May 20, 2022 at 04:49:48PM -0700, Saravana Kannan wrote:
    > > On Fri, May 20, 2022 at 4:30 PM Nathan Chancellor <nathan@kernel.org> wrote:
    > > >
    > > > Hi Saravana,
    > > >
    > > > On Fri, Apr 29, 2022 at 03:09:32PM -0700, Saravana Kannan wrote:
    > > > > The deferred probe timer that's used for this currently starts at
    > > > > late_initcall and runs for driver_deferred_probe_timeout seconds. The
    > > > > assumption being that all available drivers would be loaded and
    > > > > registered before the timer expires. This means, the
    > > > > driver_deferred_probe_timeout has to be pretty large for it to cover the
    > > > > worst case. But if we set the default value for it to cover the worst
    > > > > case, it would significantly slow down the average case. For this
    > > > > reason, the default value is set to 0.
    > > > >
    > > > > Also, with CONFIG_MODULES=y and the current default values of
    > > > > driver_deferred_probe_timeout=0 and fw_devlink=on, devices with missing
    > > > > drivers will cause their consumer devices to always defer their probes.
    > > > > This is because device links created by fw_devlink defer the probe even
    > > > > before the consumer driver's probe() is called.
    > > > >
    > > > > Instead of a fixed timeout, if we extend an unexpired deferred probe
    > > > > timer on every successful driver registration, with the expectation more
    > > > > modules would be loaded in the near future, then the default value of
    > > > > driver_deferred_probe_timeout only needs to be as long as the worst case
    > > > > time difference between two consecutive module loads.
    > > > >
    > > > > So let's implement that and set the default value to 10 seconds when
    > > > > CONFIG_MODULES=y.
    > > > >
    > > > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > > > > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
    > > > > Cc: Rob Herring <robh@kernel.org>
    > > > > Cc: Linus Walleij <linus.walleij@linaro.org>
    > > > > Cc: Will Deacon <will@kernel.org>
    > > > > Cc: Ulf Hansson <ulf.hansson@linaro.org>
    > > > > Cc: Kevin Hilman <khilman@kernel.org>
    > > > > Cc: Thierry Reding <treding@nvidia.com>
    > > > > Cc: Mark Brown <broonie@kernel.org>
    > > > > Cc: Pavel Machek <pavel@ucw.cz>
    > > > > Cc: Geert Uytterhoeven <geert@linux-m68k.org>
    > > > > Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
    > > > > Cc: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
    > > > > Cc: linux-gpio@vger.kernel.org
    > > > > Cc: linux-pm@vger.kernel.org
    > > > > Cc: iommu@lists.linux-foundation.org
    > > > > Signed-off-by: Saravana Kannan <saravanak@google.com>
    > > >
    > > > I bisected a boot hang with ARCH=s390 defconfig in QEMU down to this
    > > > change as commit 2b28a1a84a0e ("driver core: Extend deferred probe
    > > > timeout on driver registration") in next-20220520 (bisect log below).
    > > >
    > > > $ make -skj"$(nproc)" ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- defconfig bzImage
    > > >
    > > > $ timeout --foreground 15m stdbuf -oL -eL \
    > > > qemu-system-s390x \
    > > > -initrd ... \
    > > > -M s390-ccw-virtio \
    > > > -display none \
    > > > -kernel arch/s390/boot/bzImage \
    > > > -m 512m \
    > > > -nodefaults \
    > > > -serial mon:stdio
    > > > ...
    > > > [ 2.077303] In-situ OAM (IOAM) with IPv6
    > > > [ 2.077639] NET: Registered PF_PACKET protocol family
    > > > [ 2.078063] bridge: filtering via arp/ip/ip6tables is no longer available by default. Update your scripts to load br_netfilter if you need this.
    > > > [ 2.078795] Key type dns_resolver registered
    > > > [ 2.079317] cio: Channel measurement facility initialized using format extended (mode autodetected)
    > > > [ 2.081494] Discipline DIAG cannot be used without z/VM
    > > > [ 260.626363] random: crng init done
    > > > qemu-system-s390x: terminating on signal 15 from pid 3815762 (timeout)
    > > >
    > > > We have a simple rootfs available if necessary:
    > > >
    > > > https://github.com/ClangBuiltLinux/boot-utils/raw/bc0d17785eb67f1edd0ee0a134970a807895f741/images/s390/rootfs.cpio.zst
    > > >
    > > > If there is any other information I can provide, please let me know!
    > >
    > > Hmm... strange. Can you please try the following command line options
    > > and tell me which of these has the issue and which don't?
    >
    > Sure thing!
    >
    > > 1) deferred_probe_timeout=0
    >
    > No issue.
    >
    > > 2) deferred_probe_timeout=1
    > > 3) deferred_probe_timeout=300
    >
    > Both of these appear to hang in the same way, I let each sit for five
    > minutes.

    Strange that a sufficiently large timeout isn't helping. Is it trying
    to boot off a network mount? I'll continue looking into this next
    week.

    -Saravana

    >
    > Cheers,
    > Nathan

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