IOMMU core doesn't detach device from the default domain before calling
->iommu_remove_device, so check that and do the proper cleanup or
warn if device is still attached to non-default domain.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

This patch prepares Exynos IOMMU driver for deferred probing
support. Once it gets added, of_xlate() callback might be called
more than once for the same SYSMMU controller and master device
(for example it happens when masters device driver fails with
EPROBE_DEFER). This patch adds a check, which ensures that SYSMMU
controller is added to its master device (owner) only once.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Add a simple checks for dma_map_single() return value to make DMA-debug
checker happly. Exynos IOMMU on Samsung Exynos SoCs always use device,
which has linear DMA mapping ops (dma address is equal to physical memory
address), so no failures are returned from dma_map_single().

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Add master device name to default IOMMU fault message to make easier to
find which device triggered the fault. While at it, move printing some
information (like page table base and first level entry addresses) to
dev_dbg(), because those are typically not very useful for typical device
driver user/developer not equipped with hardware debugging tools.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

This patch uses recently introduced device dependency links to track the
runtime pm state of the master's device. The goal is to let SYSMMU
controller device's runtime PM to follow the runtime PM state of the
respective master's device. This way each SYSMMU controller is active
only when its master's device is active and can properly restore or save
its state instead on runtime PM transition of master's device.
This approach replaces old behavior, when SYSMMU controller was set to
runtime active once after attaching to the master device. In the new
approach SYSMMU controllers no longer prevents respective power domains
to be turned off when master's device is not being used.

This patch reduces total power consumption of idle system, because most
power domains can be finally turned off. For example, on Exynos 4412
based Odroid U3 this patch reduces power consuption from 136mA to 130mA
at 5V (by 4.4%).

The dependency links also enforce proper order of suspending/restoring
devices during system sleep transition, so there is no more need to use
LATE_SYSTEM_SLEEP_PM_OPS-based workaround for ensuring that SYSMMUs are
suspended after their master devices.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

This patch adds runtime pm implementation, which is based on previous
suspend/resume code. SYSMMU controller is now being enabled/disabled mainly
from the runtime pm callbacks. System sleep callbacks relies on generic
pm_runtime_force_suspend/pm_runtime_force_resume helpers. To ensure
internal state consistency, additional lock for runtime pm transitions
was introduced.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

This patch reworks locking in the exynos_iommu_attach/detach_device
functions to ensure that all entries of the sysmmu_drvdata and
exynos_iommu_owner structure are updated under the respective spinlocks,
while runtime pm functions are called without any spinlocks held.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

To avoid possible races, set master device pointer in each SYSMMU
controller once on boot. Suspend/resume callbacks now properly relies on
the configured iommu domain to enable or disable SYSMMU controller.
While changing the code, also update the sleep debug messages and make
them conditional.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Remove remaining leftovers of the ref-count related code in the
__sysmmu_enable/disable functions inline __sysmmu_enable/disable_nocount
to them. Suspend/resume callbacks now checks if master device is set for
given SYSMMU controller instead of relying on the activation count.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

__sysmmu_enable/disable functions were designed to do ref-count based
operations, but current code always calls them only once, so the code for
checking the conditions and invalid conditions can be simply removed
without any influence to the driver operation.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Remove excessive, useless debug about skipping TLB invalidation, which
is a normal situation when more aggressive power management is enabled.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

This patch add support for page access protection bits. Till now this
feature was disabled and Exynos SYSMMU always mapped pages as read/write.
Now page access bits are set according to the protection bits provided
in iommu_map(), so Exynos SYSMMU is able to detect incorrect access to
mapped pages. Exynos SYSMMU earlier than v5 doesn't support write-only
mappings, so pages with such protection bits are mapped as read/write.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Few architectures like x86, ia64 and s390 derive the cache topology and
all the properties using a specific architected mechanism while some
other architectures like powerpc all those information id derived from
the device tree.

On ARM, both the mechanism is used. While all the cache properties can
be derived in a architected way, it needs to rely on device tree to get
the cache topology information.

However there are few platforms where this architected mechanism is
broken and the device tree properties can be used to override these
incorrect values.

This patch adds support for overriding the cache properties values to
the values specified in the device tree.

Cc: Alex Van Brunt <avanbrunt@nvidia.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This cleanup patch just adds pr_fmt style logging for cacheinfo.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

ARM64 enables both CONFIG_OF and CONFIG_ACPI and the firmware can pass
both ACPI tables and the device tree. Based on the kernel parameter, one
of the two will be chosen. If acpi is enabled, then device tree is not
unflattened.

Currently ARM64 platforms report:
"
	Failed to find cpu0 device node
	Unable to detect cache hierarchy from DT for CPU 0
"
which is incorrect when booting with ACPI. Also latest ACPI v6.1 has no
support for cache properties/hierarchy.

This patch adds check for unflattened device tree and also returns as
"not supported" if ACPI is runtime enabled.

It also removes the reference to DT from the error message as the cache
hierarchy can be detected from the firmware(OF/DT/ACPI)

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

With CONFIG_OF enabled on x86, we get the following error on boot:
"
	Failed to find cpu0 device node
 	Unable to detect cache hierarchy from DT for CPU 0
"
and the cacheinfo fails to get populated in the corresponding sysfs
entries. This is because cache_setup_of_node looks for of_node for
setting up the shared cpu_map without checking that it's already
populated in the architecture specific callback.

In order to indicate that the shared cpu_map is already populated, this
patch introduces a boolean `cpu_map_populated` in struct cpu_cacheinfo
that can be used by the generic code to skip cache_shared_cpu_map_setup.

This patch also sets that boolean for x86.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This test module tries to test asynchronous driver probing by having a
driver that sleeps for an extended period of time (5 secs) in its
probe() method. It measures the time needed to register this driver
(with device already registered) and a new device (with driver already
registered). The module will fail to load if the time spent in register
call is more than half the probing sleep time.

As a sanity check the driver will then try to synchronously register
driver and device and fail if registration takes less than half of the
probing sleep time.

Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
Reviewed-by: Olof Johansson <olofj@chromium.org>
Signed-off-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

It is sometimes useful to know that a device is on the deferred probe
list rather than, say, not having a driver available.  Expose this
information to user-space.

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Pull i2c fix from Wolfram Sang:
 "A bugfix for the I2C core fixing a (rare) race condition"

* 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux:
  i2c: core: fix NULL pointer dereference under race condition

Merge branches 'sched-urgent-for-linus' and 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull stack vmap fixups from Thomas Gleixner:
 "Two small patches related to sched_show_task():

   - make sure to hold a reference on the task stack while accessing it

   - remove the thread_saved_pc printout

  .. and add a sanity check into release_task_stack() to catch problems
  with task stack references"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/core: Remove pointless printout in sched_show_task()
  sched/core: Fix oops in sched_show_task()

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  fork: Add task stack refcounting sanity check and prevent premature task stack freeing

Pull MD fixes from Shaohua Li:
 "There are several bug fixes queued:

   - fix raid5-cache recovery bugs

   - fix discard IO error handling for raid1/10

   - fix array sync writes bogus position to superblock

   - fix IO error handling for raid array with external metadata"

* tag 'md/4.9-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/shli/md:
  md: be careful not lot leak internal curr_resync value into metadata. -- (all)
  raid1: handle read error also in readonly mode
  raid5-cache: correct condition for empty metadata write
  md: report 'write_pending' state when array in sync
  md/raid5: write an empty meta-block when creating log super-block
  md/raid5: initialize next_checkpoint field before use
  RAID10: ignore discard error
  RAID1: ignore discard error

Pull SCSI fixes from James Bottomley:
 "Two more important data integrity fixes related to RAID device drivers
  which wrongly throw away the SYNCHRONIZE CACHE command in the non-RAID
  path and a memory leak in the scsi_debug driver"

* tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
  scsi: arcmsr: Send SYNCHRONIZE_CACHE command to firmware
  scsi: scsi_debug: Fix memory leak if LBP enabled and module is unloaded
  scsi: megaraid_sas: Fix data integrity failure for JBOD (passthrough) devices

Pull input subsystem updates from Dmitry Torokhov.

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input:
  Input: psmouse - cleanup Focaltech code
  Input: i8042 - add XMG C504 to keyboard reset table

Pull FireWire (IEEE 1394) fixes from Stefan Richter:

 - add missing input validation to the firewire-net driver. Invalid
   IP-over-1394 encapsulation headers could trigger buffer overflows
   (CVE 2016-8633).

 - IP-over-1394 link fragmentation headers were read and written
   incorrectly, breaking fragmented RX/TX with other OS's stacks.

* tag 'firewire-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/ieee1394/linux1394:
  firewire: net: fix fragmented datagram_size off-by-one
  firewire: net: guard against rx buffer overflows

Pull media fixes from Mauro Carvalho Chehab:
 "A series of fixup patches meant to fix the usage of DMA on stack, plus
  one warning fixup"

* tag 'media/v4.9-3' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (32 commits)
  [media] radio-bcm2048: don't ignore errors
  [media] pctv452e: fix semicolon.cocci warnings
  [media] flexcop-usb: don't use stack for DMA
  [media] stk-webcam: don't use stack for DMA
  [media] s2255drv: don't use stack for DMA
  [media] cpia2_usb: don't use stack for DMA
  [media] digitv: handle error code on RC query
  [media] dw2102: return error if su3000_power_ctrl() fails
  [media] nova-t-usb2: handle error code on RC query
  [media] technisat-usb2: use DMA buffers for I2C transfers
  [media] pctv452e: don't call BUG_ON() on non-fatal error
  [media] pctv452e: don't do DMA on stack
  [media] nova-t-usb2: don't do DMA on stack
  [media] gp8psk: don't go past the buffer size
  [media] gp8psk: don't do DMA on stack
  [media] dtv5100: don't do DMA on stack
  [media] dtt200u: handle USB control message errors
  [media] dtt200u: don't do DMA on stack
  [media] dtt200u-fe: handle errors on USB control messages
  [media] dtt200u-fe: don't do DMA on stack
  ...

Pull PCI fixes from Bjorn Helgaas:

 - fix for a Qualcomm driver issue that causes a use-before-set crash

 - fix for DesignWare iATU unroll support that causes external aborts
   when enabling the host bridge

* tag 'pci-v4.9-fixes-2' of git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci:
  PCI: designware: Check for iATU unroll support after initializing host
  PCI: qcom: Fix pp->dev usage before assignment

Pull MTD fixes from Brian Norris:

 - MAINTAINERS updates to reflect some new maintainers/submaintainers.

   We have some great volunteers who've been developing and reviewing
   already. We're going to try a group maintainership model, so
   eventually you'll probably see pull requests from people besides me.

 - NAND fixes from Boris:
    "Three simple fixes:

      - fix a non-critical bug in the gpmi driver
      - fix a bug in the 'automatic NAND timings selection' feature
        introduced in 4.9-rc1
      - fix a false positive uninitialized-var warning"

* tag 'for-linus-20161104' of git://git.infradead.org/linux-mtd:
  mtd: mtk: avoid warning in mtk_ecc_encode
  mtd: nand: Fix data interface configuration logic
  mtd: nand: gpmi: disable the clocks on errors
  MAINTAINERS: add more people to the MTD maintainer team
  MAINTAINERS: add a maintainer for the SPI NOR subsystem

Pull MMC fixes from Ulf Hansson:
 "MMC host:

   - sdhci-msm: Fix error path in probe
   - dw_mmc-pltfm: Avoid NULL pointer dereference"

* tag 'mmc-v4.9-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/ulfh/mmc:
  mmc: sdhci-msm: Fix error return code in sdhci_msm_probe()
  mmc: dw_mmc-pltfm: fix the potential NULL pointer dereference

Pull GPIO fixes from Linus Walleij:
 "Some GPIO fixes for the v4.9 series:

   - Fix a nasty file descriptor leak when getting line handles.

   - A fix for a cleanup that seemed innocent but created a problem for
     drivers instantiating several gpiochips for one single OF node.

   - Fix a unpredictable problem using irq_domain_simple() in the mvebu
     driver by converting it to a lineas irqdomain"

* tag 'gpio-v4.9-3' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-gpio:
  gpio/mvebu: Use irq_domain_add_linear
  gpio: of: fix GPIO drivers with multiple gpio_chip for a single node
  gpio: GPIO_GET_LINE{HANDLE,EVENT}_IOCTL: Fix file descriptor leak

Pull nfsd bugfixes from Bruce Fields:
 "Fixes for some recent regressions including fallout from the vmalloc'd
  stack change (after which we can no longer encrypt stuff on the
  stack)"

* tag 'nfsd-4.9-1' of git://linux-nfs.org/~bfields/linux:
  nfsd: Fix general protection fault in release_lock_stateid()
  svcrdma: backchannel cannot share a page for send and rcv buffers
  sunrpc: fix some missing rq_rbuffer assignments
  sunrpc: don't pass on-stack memory to sg_set_buf
  nfsd: move blocked lock handling under a dedicated spinlock

Pull btrfs fixes from Chris Mason:
 "Some fixes that Dave Sterba collected.  We held off on these last week
  because I was focused on the memory corruption testing"

* 'for-4.9-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux:
  btrfs: fix WARNING in btrfs_select_ref_head()
  Btrfs: remove some no-op casts
  btrfs: pass correct args to btrfs_async_run_delayed_refs()
  btrfs: make file clone aware of fatal signals
  btrfs: qgroup: Prevent qgroup->reserved from going subzero
  Btrfs: kill BUG_ON in do_relocation

Pull overlayfs fixes from Miklos Szeredi:
 "Fix two more POSIX ACL bugs introduced in 4.8 and add a missing fsync
  during copy up to prevent possible data loss"

* 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs:
  ovl: fsync after copy-up
  ovl: fix get_acl() on tmpfs
  ovl: update S_ISGID when setting posix ACLs

Pull drm fixes from Dave Airlie:
 "Fixes for amdgpu, radeon, intel, imx and virtio-gpu.

  This is a bit larger than I'd like, but I had some stuff I meant to
  send for -rc3 but was waiting for the PAT regression fix to land. So
  this is really fixes for rc3 and rc4 in one go.

  There are a set of fixes for an oops we've been seeing around MST
  display unplug, along with more suspend/resume and shutdown fixes for
  amdgpu, one power management follow on fix for nouveau, and set of imx
  fixes, and a single virtio-gpu regression fix"

* tag 'drm-fixes-for-v4.9-rc4' of git://people.freedesktop.org/~airlied/linux: (54 commits)
  virtio-gpu: fix vblank events
  drm/nouveau/acpi: fix check for power resources support
  drm/i915: Fix SKL+ 90/270 degree rotated plane coordinate computation
  drm/i915: Remove two invalid warns
  drm/i915: Rotated view does not need a fence
  drm/i915/fbc: fix CFB size calculation for gen8+
  drm: i915: Wait for fences on new fb, not old
  drm/i915: Clean up DDI DDC/AUX CH sanitation
  drm/i915: Respect alternate_aux_channel for all DDI ports
  drm/i915/gen9: fix watermarks when using the pipe scaler
  drm/i915: Fix mismatched INIT power domain disabling during suspend
  drm/i915: fix a read size argument
  drm/i915: Use fence_write() from rpm resume
  drm/i915/gen9: fix DDB partitioning for multi-screen cases
  drm/i915: workaround sparse warning on variable length arrays
  drm/i915: keep declarations in i915_drv.h
  drm/amd/powerplay: fix bug get wrong evv voltage of Polaris.
  drm/amdgpu/si_dpm: workaround for SI kickers
  drm/radeon/si_dpm: workaround for SI kickers
  drm/amdgpu: fix s3 resume back, uvd dpm randomly can't disable.
  ...

dw_pcie_iatu_unroll_enabled() reads a dbi_base register.  Reading any
dbi_base register before pp->ops->host_init has been called causes
"imprecise external abort" on platforms like ARTPEC-6, where the PCIe
module is disabled at boot and first enabled in pp->ops->host_init.  Move
dw_pcie_iatu_unroll_enabled() to dw_pcie_setup_rc(), since it is after
pp->ops->host_init, but before pp->iatu_unroll_enabled is actually used.

Fixes: a0601a47

 ("PCI: designware: Add iATU Unroll feature")
Tested-by: James Le Cuirot <chewi@gentoo.org>
Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Joao Pinto <jpinto@synopsys.com>
Acked-by: Olof Johansson <olof@lixom.net>

Pull KVM updates from Paolo Bonzini:
 "One NULL pointer dereference, and two fixes for regressions introduced
  during the merge window.

  The rest are fixes for MIPS, s390 and nested VMX"

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  kvm: x86: Check memopp before dereference (CVE-2016-8630)
  kvm: nVMX: VMCLEAR an active shadow VMCS after last use
  KVM: x86: drop TSC offsetting kvm_x86_ops to fix KVM_GET/SET_CLOCK
  KVM: x86: fix wbinvd_dirty_mask use-after-free
  kvm/x86: Show WRMSR data is in hex
  kvm: nVMX: Fix kernel panics induced by illegal INVEPT/INVVPID types
  KVM: document lock orders
  KVM: fix OOPS on flush_work
  KVM: s390: Fix STHYI buffer alignment for diag224
  KVM: MIPS: Precalculate MMIO load resume PC
  KVM: MIPS: Make ERET handle ERL before EXL
  KVM: MIPS: Fix lazy user ASID regenerate for SMP

Pull MIPS fixes from Ralf Baechle:
 "A set of MIPS fixes for 4.9:

   - lots of fixes for printk continuations
   - six fixes for FP related code.
   - fix max_low_pfn with disabled highmem
   - fix KASLR handling of NULL FDT and KASLR for generic kernels
   - fix build of compressed image
   - provide default mips_cpc_default_phys_base to ignore CPC
   - fix reboot on Malta"

* 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus:
  MIPS: Fix max_low_pfn with disabled highmem
  MIPS: Correct MIPS I FP sigcontext layout
  MIPS: Fix ISA I/II FP signal context offsets
  MIPS: Remove FIR from ISA I FP signal context
  MIPS: Fix ISA I FP sigcontext access violation handling
  MIPS: Fix FCSR Cause bit handling for correct SIGFPE issue
  MIPS: ptrace: Also initialize the FP context on individual FCSR writes
  MIPS: dump_tlb: Fix printk continuations
  MIPS: Fix __show_regs() output
  MIPS: traps: Fix output of show_code
  MIPS: traps: Fix output of show_stacktrace
  MIPS: traps: Fix output of show_backtrace
  MIPS: Fix build of compressed image
  MIPS: generic: Fix KASLR for generic kernel.
  MIPS: KASLR: Fix handling of NULL FDT
  MIPS: Malta: Fixup reboot
  MIPS: CPC: Provide default mips_cpc_default_phys_base to ignore CPC

Pull parisc updates from Helge Deller:
 "The first three patches are trivial and add some required KERN_CONT,
  ignore the new pkey syscalls on parisc and use the LINUX_GATEWAY_ADDR
  define instead of hardcoded values.

  The two patches from Dave Anglin are important.

  The first one avoids trashing the sr2 and sr3 space registers in the
  Light-weight syscall path. Especially the usage of sr3 is critical
  since it may get trashed by the interrupt handler.

  The second patch is even more important and tagged for stable series.
  It protects one critical section in the syscall entry path by
  disabling local interrupts. Without disabling interrupts, the sr7
  space register may not be in sync with the current stack setup and
  thus an incoming hardware interrupt may destroy memory in random
  userspace areas"

* 'parisc-4.9-3' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux:
  parisc: Ignore the pkey system calls for now
  parisc: Use LINUX_GATEWAY_ADDR define instead of hardcoded value
  parisc: Ensure consistent state when switching to kernel stack at syscall entry
  parisc: Avoid trashing sr2 and sr3 in LWS code
  parisc: use KERN_CONT when printing device inventory

Race condition between registering an I2C device driver and
deregistering an I2C adapter device which is assumed to manage that
I2C device may lead to a NULL pointer dereference due to the
uninitialized list head of driver clients.

The root cause of the issue is that the I2C bus may know about the
registered device driver and thus it is matched by bus_for_each_drv(),
but the list of clients is not initialized and commonly it is NULL,
because I2C device drivers define struct i2c_driver as static and
clients field is expected to be initialized by I2C core:

  i2c_register_driver()             i2c_del_adapter()
    driver_register()                 ...
      bus_add_driver()                ...
        ...                           bus_for_each_drv(..., __process_removed_adapter)
      ...                               i2c_do_del_adapter()
    ...                                   list_for_each_entry_safe(..., &driver->clients, ...)
    INIT_LIST_HEAD(&driver->clients);

To solve the problem it is sufficient to do clients list head
initialization before calling driver_register().

The problem was found while using an I2C device driver with a sluggish
registration routine on a bus provided by a physically detachable I2C
master controller, but practically the oops may be reproduced under
the race between arbitraty I2C device driver registration and managing
I2C bus device removal e.g. by unbinding the latter over sysfs:

% echo 21a4000.i2c > /sys/bus/platform/drivers/imx-i2c/unbind
  Unable to handle kernel NULL pointer dereference at virtual address 00000000
  Internal error: Oops: 17 [#1] SMP ARM
  CPU: 2 PID: 533 Comm: sh Not tainted 4.9.0-rc3+ #61
  Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
  task: e5ada400 task.stack: e4936000
  PC is at i2c_do_del_adapter+0x20/0xcc
  LR is at __process_removed_adapter+0x14/0x1c
  Flags: NzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
  Control: 10c5387d  Table: 35bd004a  DAC: 00000051
  Process sh (pid: 533, stack limit = 0xe4936210)
  Stack: (0xe4937d28 to 0xe4938000)
  Backtrace:
  [<c0667be0>] (i2c_do_del_adapter) from [<c0667cc0>] (__process_removed_adapter+0x14/0x1c)
  [<c0667cac>] (__process_removed_adapter) from [<c0516998>] (bus_for_each_drv+0x6c/0xa0)
  [<c051692c>] (bus_for_each_drv) from [<c06685ec>] (i2c_del_adapter+0xbc/0x284)
  [<c0668530>] (i2c_del_adapter) from [<bf0110ec>] (i2c_imx_remove+0x44/0x164 [i2c_imx])
  [<bf0110a8>] (i2c_imx_remove [i2c_imx]) from [<c051a838>] (platform_drv_remove+0x2c/0x44)
  [<c051a80c>] (platform_drv_remove) from [<c05183d8>] (__device_release_driver+0x90/0x12c)
  [<c0518348>] (__device_release_driver) from [<c051849c>] (device_release_driver+0x28/0x34)
  [<c0518474>] (device_release_driver) from [<c0517150>] (unbind_store+0x80/0x104)
  [<c05170d0>] (unbind_store) from [<c0516520>] (drv_attr_store+0x28/0x34)
  [<c05164f8>] (drv_attr_store) from [<c0298acc>] (sysfs_kf_write+0x50/0x54)
  [<c0298a7c>] (sysfs_kf_write) from [<c029801c>] (kernfs_fop_write+0x100/0x214)
  [<c0297f1c>] (kernfs_fop_write) from [<c0220130>] (__vfs_write+0x34/0x120)
  [<c02200fc>] (__vfs_write) from [<c0221088>] (vfs_write+0xa8/0x170)
  [<c0220fe0>] (vfs_write) from [<c0221e74>] (SyS_write+0x4c/0xa8)
  [<c0221e28>] (SyS_write) from [<c0108a20>] (ret_fast_syscall+0x0/0x1c)

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org