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Date:   Mon, 23 May 2022 15:14:14 -0700
From:   Nathan Chancellor <nathan@kernel.org>
To:     Saravana Kannan <saravanak@google.com>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Rob Herring <robh@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Will Deacon <will@kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Kevin Hilman <khilman@kernel.org>,
        Thierry Reding <treding@nvidia.com>,
        Mark Brown <broonie@kernel.org>, Pavel Machek <pavel@ucw.cz>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
        Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
        linux-gpio@vger.kernel.org, linux-pm@vger.kernel.org,
        iommu@lists.linux-foundation.org, kernel-team@android.com,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-s390@vger.kernel.org
Subject: Re: [PATCH v1] driver core: Extend deferred probe timeout on driver
 registration
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On Mon, May 23, 2022 at 01:04:03PM -0700, Saravana Kannan wrote:
> On Mon, May 23, 2022 at 8:17 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > On Fri, May 20, 2022 at 05:15:55PM -0700, Saravana Kannan wrote:
> > > 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.
> >
> > I don't think so, it seems like doing that requires some extra flags
> > that we do not have:
> >
> > https://wiki.qemu.org/Features/S390xNetworkBoot
> >
> > If you need any additional information or want something tested, please
> > let me know!
> 
> I'll try to get qemu going on my end, but I'm not too confident I'll
> be able to get to it in a timely fashion. So if you can help figure
> out where this boot process is hanging, that'd be very much
> appreciated.

Sure thing! Information included below, I am more than happy to continue
to test and debug as you need.

> Couple of suggestions for debugging:
> 
> Can you add a log to "wait_for_device_probe()" and see if that's
> getting called right before the boot process hangs? If it does, can
> you get a stacktrace (I just add a WARN_ON(1) when I need a stack
> trace)? It's unlikely this is the case because
> deferred_probe_timeout=1 still causes an issue for you, but I'd be
> good to rule out.

If I add a pr_info() call at the top of wait_for_device_probe(), I see
it right before the process hangs. Adding WARN_ON(1) right below that
reveals dasd_eckd_init() in drivers/s390/block/dasd_eckd.c calls
wait_for_device_probe():

[    4.610397] ------------[ cut here ]------------
[    4.610520] WARNING: CPU: 0 PID: 1 at drivers/base/dd.c:742 wait_for_device_probe+0x28/0x110
[    4.611134] Modules linked in:
[    4.611593] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.18.0-next-20220523-dirty #1
[    4.611830] Hardware name: QEMU 8561 QEMU (KVM/Linux)
[    4.612017] Krnl PSW : 0704c00180000000 0000000000ce4b3c (wait_for_device_probe+0x2c/0x110)
[    4.612258]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3
[    4.612387] Krnl GPRS: 80000000fffff071 0000000000000027 000000000000000c 00000000017f91d8
[    4.612457]            00000000fffff071 00000000017f9218 0000000001a655a0 0000000000000006
[    4.612521]            0000000000000002 0000000001965810 00000000019d51a0 0000000000000000
[    4.612585]            0000000002218000 000000000125bcc8 0000000000ce4b38 000003800000bc80
[    4.614814] Krnl Code: 0000000000ce4b2c: e3e0f0980024        stg     %r14,152(%r15)
[    4.614814]            0000000000ce4b32: c0e5ffff94cb        brasl   %r14,0000000000cd74c8
[    4.614814]           #0000000000ce4b38: af000000            mc      0,0
[    4.614814]           >0000000000ce4b3c: c0100054d1fa        larl    %r1,000000000177ef30
[    4.614814]            0000000000ce4b42: e31010000012        lt      %r1,0(%r1)
[    4.614814]            0000000000ce4b48: a784002d            brc     8,0000000000ce4ba2
[    4.614814]            0000000000ce4b4c: d727f0a0f0a0        xc      160(40,%r15),160(%r15)
[    4.614814]            0000000000ce4b52: 41b0f0a0            la      %r11,160(%r15)
[    4.615698] Call Trace:
[    4.616559]  [<0000000000ce4b3c>] wait_for_device_probe+0x2c/0x110
[    4.616744] ([<0000000000ce4b38>] wait_for_device_probe+0x28/0x110)
[    4.616841]  [<000000000196593e>] dasd_eckd_init+0x12e/0x178
[    4.616913]  [<0000000000100936>] do_one_initcall+0x46/0x1e8
[    4.616983]  [<0000000001920706>] do_initcalls+0x126/0x150
[    4.617046]  [<000000000192095e>] kernel_init_freeable+0x1ae/0x1f0
[    4.617110]  [<0000000000ce85a6>] kernel_init+0x2e/0x168
[    4.617171]  [<0000000000103320>] __ret_from_fork+0x40/0x58
[    4.617233]  [<0000000000cf5eaa>] ret_from_fork+0xa/0x40
[    4.617352] Last Breaking-Event-Address:
[    4.617393]  [<0000000000e0e098>] __s390_indirect_jump_r14+0x0/0xc
[    4.617481] ---[ end trace 0000000000000000 ]---

> Let's try to rule out if deferred_probe_extend_timeout() is causing
> some issues. So, without my patch, what happens if you set:
> deferred_probe_timeout=1
> deferred_probe_timeout=300

At commit 6ee60e9c9f2f ("MAINTAINERS: add Russ Weight as a firmware
loader maintainer"), both deferred_probe_timeout=1 and
deferred_probe_timeout=300 hang the boot.

> If deferred_probe_timeout=1 causes an issue even without my patch,
> then in addition, can you try commenting out the call to
> fw_devlink_drivers_done() inside deferred_probe_timeout_work_func()
> and try again?

Sure, that does not appear to make a difference with
deferred_probe_timeout=1.

Cheers,
Nathan