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SubjectRe: [PATCH v2 0/9] deferred_probe_timeout logic clean up
Hi Saravana,

On Wed, Jun 8, 2022 at 6:17 AM Saravana Kannan <saravanak@google.com> wrote:
> On Tue, Jun 7, 2022 at 5:55 PM Saravana Kannan <saravanak@google.com> wrote:
> > On Tue, Jun 7, 2022 at 11:13 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > On Wed, Jun 1, 2022 at 12:46 PM Saravana Kannan <saravanak@google.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:
> > >
> > > [ OK ] Started D-Bus System Message Bus.
> > > Unable to handle kernel NULL pointer dereference at virtual
> > > address 0000000000000000
> > > Unable to handle kernel NULL pointer dereference at virtual
> > > address 0000000000000000
> > > Mem abort info:
> > > ESR = 0x0000000096000004
> > > Mem abort info:
> > > ESR = 0x0000000096000004
> > > EC = 0x25: DABT (current EL), IL = 32 bits
> > > SET = 0, FnV = 0
> > > EC = 0x25: DABT (current EL), IL = 32 bits
> > > EA = 0, S1PTW = 0
> > > FSC = 0x04: level 0 translation fault
> > > SET = 0, FnV = 0
> > > Data abort info:
> > > ISV = 0, ISS = 0x00000004
> > > EA = 0, S1PTW = 0
> > > FSC = 0x04: level 0 translation fault
> > > CM = 0, WnR = 0
> > > user pgtable: 4k pages, 48-bit VAs, pgdp=000000004ec45000
> > > [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
> > > Data abort info:
> > > Internal error: Oops: 96000004 [#1] PREEMPT SMP
> > > CPU: 0 PID: 374 Comm: v4l_id Tainted: G W
> > > 5.19.0-rc1-arm64-renesas-00799-gc13c3e49e8bd #1660
> > > ISV = 0, ISS = 0x00000004
> > > Hardware name: Renesas Ebisu-4D board based on r8a77990 (DT)
> > > pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> > > CM = 0, WnR = 0
> > > pc : subdev_open+0x8c/0x128
> > > lr : subdev_open+0x78/0x128
> > > sp : ffff80000aadba60
> > > x29: ffff80000aadba60 x28: 0000000000000000 x27: ffff80000aadbc58
> > > x26: 0000000000020000 x25: ffff00000b3aaf00 x24: 0000000000000000
> > > x23: ffff00000c331c00 x22: ffff000009aa61b8 x21: ffff000009aa6000
> > > x20: ffff000008bae3e8 x19: ffff00000c3fe200 x18: 0000000000000000
> > > x17: ffff800076945000 x16: ffff800008004000 x15: 00008cc6bf550c7c
> > > x14: 000000000000038f x13: 000000000000001a x12: ffff00007fba8618
> > > x11: 0000000000000001 x10: 0000000000000000 x9 : ffff800009253954
> > > x8 : ffff00000b3aaf00 x7 : 0000000000000004 x6 : 000000000000001a
> > > x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000001
> > > x2 : 0000000100000001 x1 : 0000000000000000 x0 : 0000000000000000
> > > Call trace:
> > > subdev_open+0x8c/0x128
>
> After disassembling the code on my end (with slightly different
> config) and looking at 0x8c from the start of the function, I'm pretty
> sure the NULL deref is happening here inside subdev_open()
>
> if (sd->v4l2_dev->mdev && sd->entity.graph_obj.mdev->dev) {
>
> sd->entity.graph_obj.mdev == NULL.
>
> And going by the field names, I'm guessing these are suppliers pointed
> to by "remote-endpoint". Sadly fw_devlink can't extract any dependency
> info from remote-endpoint because the devices generally point to each
> other so a cycle is detected and the probe ordering isn't enforced
> between the endpoints. We still need to parse remote-endpoint to
> detect cycles created by a combination of endpoints/other properties
> (there's a real world case in upstream).
>
> > > v4l2_open+0xa4/0x120
> > > chrdev_open+0x78/0x178
> > > do_dentry_open+0xfc/0x398
> > > vfs_open+0x28/0x30
> > > path_openat+0x584/0x9c8
> > > do_filp_open+0x80/0x108
> > > do_sys_openat2+0x20c/0x2d8
> > > user pgtable: 4k pages, 48-bit VAs, pgdp=000000004ec53000
> > > do_sys_open+0x54/0xa0
> > > __arm64_sys_openat+0x20/0x28
> > > invoke_syscall+0x40/0xf8
> > > el0_svc_common.constprop.0+0xf0/0x110
> > > do_el0_svc+0x20/0x78
> > > el0_svc+0x48/0xd0
> > > el0t_64_sync_handler+0xb0/0xb8
> > > el0t_64_sync+0x148/0x14c
> > > Code: f9405280 f9400400 b40000e0 f9400280 (f9400000)
> > > ---[ end trace 0000000000000000 ]---
> > >
> > > This only happens on the Ebisu-4D board (r8a77990-ebisu.dts).
> > > I do not see this on the Salvator-X(S) boards.
> >
> > Ok. I don't know much about either of these boards. Are they supposed
> > to be very similar?
> >
> > > Bisection shows this starts to happen with "[PATCH v2 7/9] driver core:
> > > Set fw_devlink.strict=1 by default".
> >
> > So in the series, by this point, the previous patches would have
> > deferred probe timeout set to 10s (it can get extended on new driver
> > additions of course) and once the timer expires suppliers without
> > drivers will no longer block any consumers. The only difference
> > fw_devlink.strict=1 should cause is iommus and dmas dependency being
> > treated as mandatory till the timeout expires.
> >
> > In this instance, do you have iommu drivers and dma drivers compiled
> > in or loaded as modules or not available at all? In all these case,
> > the list of devices that would end up probing eventually should be the
> > same with or without fw_devlink.strict=1. The only difference would be
> > some reordering of probes.
> >
> > So this looks to me like improper error handling/assumption in the
> > driver for this subdev device. I'm guessing one of the suppliers to
> > this subdev has a direct/indirect dependency on iommus and this subdev
> > driver is assuming that the supplier would have probed by the time
> > it's probed.
> >
> > >
> > > Adding more debug info:
> > >
> > > subdev_open:54: file v4l-subdev1
> > > Unable to handle kernel NULL pointer dereference at virtual
> > > address 0000000000000000
> > > subdev_open:54: file v4l-subdev2
> > > Unable to handle kernel NULL pointer dereference at virtual
> > > address 0000000000000000
>
> How did you get these two "subdev_open" strings? And how/why the NULL
> deref there?

I added a debug print at the top of subdev_open():

pr_info("%s:%u: file %pD\n", __func__, __LINE__, file);

The NULL deref is the actual issue.

> > > Matching the subdev using sysfs gives:
> > >
> > > /sys/devices/platform/soc/e6500000.i2c/i2c-0/0-0070/video4linux/v4l-subdev1
> > > /sys/devices/platform/soc/e6500000.i2c/i2c-0/0-0070/video4linux/v4l-subdev2
> > >
> > > The i2c device is the adi,adv7482 at address 0x70.
> >
> > I'm guessing the fix would be somewhere in this driver, but I haven't
> > dug into it. Any guesses on which of its suppliers might have a
> > direct/indirect dependency on an iommu/dma? You could also enable the
> > debug log in fw_devlink_relax_link() and see if it relaxes any link
> > where the supplier is an iommu/dma device. That might give us some
> > hints.
>
> After spending way too much time on this looking at
> drivers/media/v4l2-core, drivers/media/mc and
> drivers/media/i2c/adv748x/ code, I'm guessing the ordering issue is
> probably between "csi40:" device and the video-receiver@70 (the
> "adi,adv7482") device.
>
> Based on your points about the sysfs, I was initially digging into
> drivers/media/i2c/adv748x/adv748x-core.c. But then the parent of
> video-receiver@70 is an i2c0 that has dmas dependencies. The csi40:
> (referred to from video-controller) doesn't seem to have any iommu or
> dmas dependency. So my guess is the csi40 gets probed first and then
> assumes the video-controller is already available.
>
> Can you use this info to take a stab at debugging this further?

Thanks for looking into this, there is indeed a cyclic dependency:

i2c 0-0070: Fixing up cyclic dependency with feaa0000.csi2
i2c 0-0070: Fixing up cyclic dependency with hdmi-in
i2c 0-0070: Fixing up cyclic dependency with cvbs-in

> TL;DR is that I think this is some driver issue where it's not
> checking for one of its suppliers to be ready yet.

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").

I am bringing it up with the multi-media guys in
https://lore.kernel.org/all/20220124124858.571363-4-niklas.soderlund+renesas@ragnatech.se...

Thanks!

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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

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