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    SubjectRe: [PATCH v2 0/9] deferred_probe_timeout logic clean up
    On Tue, Jun 7, 2022 at 5:55 PM Saravana Kannan <saravanak@google.com> wrote:
    >
    > -Hideaki -- their email keeps bouncing.
    >
    > On Tue, Jun 7, 2022 at 11:13 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
    > >
    > > Hi Saravana,
    > >
    > > 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?

    > >
    > > 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?

    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.

    -Saravana

    >
    > -Saravana
    >
    > > But now I'm lost...
    > >
    > > 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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