arch/mips/generic/irq.c provides implementations of the
get_c0_compare_int() & get_c0_perfcount_int() functions, but doesn't
include the asm/time.h header which declares them. This leads to
warnings from sparse:

  arch/mips/generic/irq.c:36:5: warning: symbol 'get_c0_perfcount_int'
    was not declared. Should it be static?
  arch/mips/generic/irq.c:52:14: warning: symbol 'get_c0_compare_int'
    was not declared. Should it be static?

Fix this by including asm/time.h to get the declarations of
get_c0_compare_int() & get_c0_perfcount_int().
Signed-off-by: NPaul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: trivial@kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/17167/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/generic/init.c provides an implementation of the
plat_fdt_relocated() function, but doesn't include the asm/bootinfo.h
header which declares it. This leads to a warning from sparse:

arch/mips/generic/init.c:94:13: warning: symbol 'plat_fdt_relocated' was
  not declared. Should it be static?

Fix this by including asm/bootinfo.h to get the declaration of
plat_fdt_relocated(). We also #ifdef our definition of
plat_fdt_relocated() such that it is only provided when
CONFIG_RELOCATABLE is set, matching the header & avoiding the redundant
function for non-relocatable kernels.
Signed-off-by: NPaul Burton <paul.burton@imgtec.com>
Cc: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: trivial@kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/17166/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Besides eliminating lots of duplication this also allows allocations with
the DMA_ATTR_NON_CONSISTENT to use the CMA allocator.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17181/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Create a defconfig for the Omega2+ that reaches userspace and
allows use of the USB port.
Signed-off-by: NHarvey Hunt <harvey.hunt@imgtec.com>
Cc: robh+dt@kernel.org
Cc: mark.rutland@arm.com
Cc: john@phrozen.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17138/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

The Onion Omega2+ is an MT7688A based board that has 128MB RAM and
multiple peripherals.

The MT7688A is pin compatible with the MT7628A, although the former
supports a 1T1R antenna whereas the MT7628A supports a 2R2T antenna.
Signed-off-by: NHarvey Hunt <harvey.hunt@imgtec.com>
Cc: robh+dt@kernel.org
Cc: mark.rutland@arm.com
Cc: john@phrozen.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17137/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Enabled supported drivers, including:
    - USB PHY
    - EHCI
    - UART
Signed-off-by: NHarvey Hunt <harvey.hunt@imgtec.com>
Cc: robh+dt@kernel.org
Cc: mark.rutland@arm.com
Cc: john@phrozen.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17135/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

The VoCore2 board is a low cost MT7628A based board with 128MB RAM, 16MB
flash and multiple external peripherals.

This initial DTS provides enough support to get to userland and use the USB
port.
Signed-off-by: NHarvey Hunt <harvey.hunt@imgtec.com>
Cc: robh+dt@kernel.org
Cc: mark.rutland@arm.com
Cc: john@phrozen.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17134/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

VoCore are a manufacturer of devices such as the VoCore2.
Signed-off-by: NHarvey Hunt <harvey.hunt@imgtec.com>
Acked-by: NRob Herring <robh@kernel.org>
Cc: robh+dt@kernel.org
Cc: mark.rutland@arm.com
Cc: john@phrozen.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17132/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

The MT7628A is the successor to the MT7620 and pin compatible with the
MT7688A, although the latter supports only a 1T1R antenna rather than
a 2T2R antenna.

This commit adds support for the following features:

- UART
- USB PHY
- EHCI
- Interrupt controller
- System controller
- Memory controller
- Reset controller
Signed-off-by: NHarvey Hunt <harvey.hunt@imgtec.com>
Cc: robh+dt@kernel.org
Cc: mark.rutland@arm.com
Cc: john@phrozen.org
Cc: Harvey Hunt <harvey.hunt@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mediatek@lists.infradead.org
Patchwork: https://patchwork.linux-mips.org/patch/17133/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

This introduces threaded carddetect irqs for the db1200/db1300 boards.
Main benefit is that the broken insertion/ejection interrupt pairs
can now be better supported and debounced in software.
Signed-off-by: NManuel Lauss <manuel.lauss@gmail.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15287/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

No advanced MIPS features for Alchemy.
This patch shaves additional 43kB off the DB1300 kernel
(~0.5% size reduction).
Signed-off-by: NManuel Lauss <manuel.lauss@gmail.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15286/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Prints the devboard name in cpuinfo "machine" line.
Signed-off-by: NManuel Lauss <manuel.lauss@gmail.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15285/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

GCC-7 complains about a boolean value being used with an arithmetic
AND:

arch/mips/math-emu/cp1emu.c: In function 'cop1Emulate':
arch/mips/math-emu/cp1emu.c:838:14: warning: '~' on a boolean expression [-Wbool-operation]
  fpr = (x) & ~(cop1_64bit(xcp) == 0);    \
              ^
arch/mips/math-emu/cp1emu.c:1068:3: note: in expansion of macro 'DITOREG'
   DITOREG(dval, MIPSInst_RT(ir));
   ^~~~~~~
arch/mips/math-emu/cp1emu.c:838:14: note: did you mean to use logical not?
  fpr = (x) & ~(cop1_64bit(xcp) == 0);    \

Since cop1_64bit() returns and int, just flip the LSB.
Suggested-by: NMaciej W. Rozycki <macro@imgtec.com>
Signed-off-by: NManuel Lauss <manuel.lauss@gmail.com>
Reviewed-by: NMaciej W. Rozycki <macro@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17058/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Add devicetree nodes for the DM9000 and the ethernet power regulator.
Additionally, add a new pinctrl node for the ethernet chip's pins.
Signed-off-by: NHarvey Hunt <harvey.hunt@imgtec.com>
Cc: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Paul Cercueil <paul@crapouillou.net>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: devicetree@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16752/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Update the Ci20's defconfig to enable the JZ4780's GPIO driver.
Signed-off-by: NHarvey Hunt <harvey.hunt@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16751/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Move the NI 169445 board flattened image tree source into its own file
which is concatenated into the final image tree source used to build the
flattened image tree. Separating boards into different files will help
us to avoid conflicts as boards are added.
Signed-off-by: NPaul Burton <paul.burton@imgtec.com>
Cc: Nathan Sullivan <nathan.sullivan@ni.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16940/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Move the Boston board flattened image tree source into its own file
which is concatenated into the final image tree source used to build the
flattened image tree. Separating boards into different files will help
us to avoid conflicts as boards are added.
Signed-off-by: NPaul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16939/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

In preparation for splitting arch/mips/generic/vmlinux.its.S into
multiple files such that it doesn't become a conflict magnet as boards
are added, allow platforms to specify a list of image tree source files
which will be concatenated to form the final source used to build the
image tree.
Signed-off-by: NPaul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16938/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Define Cavium Octeon as a CPU that has support for mips32r1, mips32r2 and
mips64r1. This will affect show_cpuinfo() that will now correctly expose
mips32r1, mips32r2 and mips64r1 as supported ISAs.
Signed-off-by: NPetar Jovanovic <petar.jovanovic@rt-rk.com>
Reviewed-by: NMaciej W. Rozycki <macro@imgtec.com>
Acked-by: NDavid Daney <david.daney@cavium.com>
Cc: petar.jovanovic@imgtec.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15749/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Based on discussion with Linus remove the impossible to reach code
rather than replacing it with a BUG().
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>
Link: http://lkml.kernel.org/r/20170718140651.15973-4-ebiederm@xmission.com

Support the National Instruments 169445 board.
Signed-off-by: NNathan Sullivan <nathan.sullivan@ni.com>
Acked-by: NRob Herring <robh@kernel.org>
Cc: devicetree@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16782/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Commit a53e35db ("reset: Ensure drivers are explicit when requesting
reset lines") started to transition the reset control request API calls
to explicitly state whether the driver needs exclusive or shared reset
control behavior. Convert all drivers requesting exclusive resets to the
explicit API call so the temporary transition helpers can be removed.

No functional changes.
Signed-off-by: NPhilipp Zabel <p.zabel@pengutronix.de>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16785/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

When the upstream kernel pistachio_defconfig is built & tested on the
ci40 platform the current lack of these options leads to essentially
false failures when the RFS fails to mount.
Signed-off-by: NMatt Redfearn <matt.redfearn@imgtec.com>
Cc: James Hartley <james.hartley@sondrel.com>
Cc: Ionela Voinescu <ionela.voinescu@imgtec.com>
Cc: James Hartley <james.hartley@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16763/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Commit a7be6e5a ("mm: drop useless local parameters of
__register_one_node()") removes the last user of parent_node().

The parent_node() macros in both IP27 and Loongson64 are unnecessary.

Remove it for cleanup.
Reported-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NDou Liyang <douly.fnst@cn.fujitsu.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16873/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Compile USB driver statically, enable EDAC driver, and remove
deprecated options.
Signed-off-by: NSteven J. Hill <steven.hill@cavium.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16795/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Commit 1a3d5957 ("MIPS: Tidy up FPU context switching") removed
usage of ST_OFF, leaving it behind as dead code. Commit 828d1e4e
("MIPS: Remove dead define of ST_OFF") then removed the definition of
ST_OFF from r4k_switch.S as a cleanup. However the unused definition of
ST_OFF has been left behind in r2300_switch.S. Remove it.
Signed-off-by: NPaul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16239/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Move _save_fp(), _restore_fp() & _init_fpu() out of r2300_switch.S &
into r2300_fpu.S. This logically places all FP-related asm code into
r2300_fpu.S & provides consistency with R4K after the preceding commit.

Besides cleaning up this will be useful for later patches which disable
FP support.

[ralf@linux-mips.org: Fixed build issues reported by Arnd Bergmann
<arnd@arndb.de>]
Signed-off-by: NPaul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16238/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Move _save_fp(), _restore_fp(), _save_msa(), _restore_msa(),
_init_msa_upper() & _init_fpu() out of r4k_switch.S & into r4k_fpu.S.
This allows us to clean up the way in which Octeon includes the default
r4k implementations of these FP functions despite replacing resume(),
and makes CONFIG_R4K_FPU more straightforwardly represent all
configurations that have an R4K-style FPU, including Octeon.

Besides cleaning up this will be useful for later patches which disable
FP support.

[ralf@linux-mips.org: Fixed build issues reported by Arnd Bergmann
<arnd@arndb.de>]
Signed-off-by: NPaul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16237/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

The kernel contains a small amount of incomplete code aimed at
supporting old R6000 CPUs. This is:

  - Unused, as no machine selects CONFIG_SYS_HAS_CPU_R6000.

  - Broken, since there are glaring errors such as r6000_fpu.S moving
    the FCSR register to t1, then ignoring it & instead saving t0 into
    struct sigcontext...

  - A maintenance headache, since it's code that nobody can test which
    nevertheless imposes constraints on code which it shares with other
    machines.

Remove this incomplete & broken R6000 CPU support in order to clean up
and in preparation for changes which will no longer need to consider
dragging the pretense of R6000 support along with them.
Signed-off-by: NPaul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16236/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

The r2_decoder_tables are never modified. They are arrays of constant
values and as such should be declared const.

This change saves 256 bytes of kernel text, and 128 bytes of kernel data
(384 bytes total) on a 32r6el_defconfig (with SMP disabled)
Before:
   text	   data	    bss	    dec	    hex	filename
5576221	1080804	 267040	6924065	 69a721	vmlinux
After:
   text	   data	    bss	    dec	    hex	filename
5575965	1080676	 267040	6923681	 69a5a1	vmlinux
Signed-off-by: NMatt Redfearn <matt.redfearn@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15289/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

smp_ops providers do not modify their ops structures, so they should be
made const for robustness. Since currently the MIPS kernel is not mapped
with memory protection, this does not in itself provide any security
benefit, but it still makes sense to make this change.

There are also slight code size efficincies from the structure being
made read-only, saving 128 bytes of kernel text on a
pistachio_defconfig.
Before:
   text	   data	    bss	    dec	    hex	filename
7187239	1772752	 470224	9430215	 8fe4c7	vmlinux
After:
   text	   data	    bss	    dec	    hex	filename
7187111	1772752	 470224	9430087	 8fe447	vmlinux
Signed-off-by: NMatt Redfearn <matt.redfearn@imgtec.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Kevin Cernekee <cernekee@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Doug Ledford <dledford@redhat.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Joe Perches <joe@perches.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven J. Hill <steven.hill@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16784/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Remove options which do not exist anymore:
 - CPU_FREQ_DEBUG is gone since commit 2d06d8c4  ("[CPUFREQ] use
   dynamic debug instead of custom infrastructure").

 - ECONET is gone since commit 349f29d8 ("econet: remove ancient bug
   ridden protocol");

 - IPDDP_DECAP is gone since commit 9b5645b5 ("appletalk: remove
   "config IPDDP_DECAP"");
Signed-off-by: NKrzysztof Kozlowski <krzk@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16770/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Now that we have a custom printf format specifier, convert users of
full_name to use %pOF instead. This is preparation to remove storing
of the full path string for each node.
Signed-off-by: NRob Herring <robh@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16783/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

Pull IOMMU fix from Joerg Roedel:
 "Another fix, this time in common IOMMU sysfs code.

  In the conversion from the old iommu sysfs-code to the
  iommu_device_register interface, I missed to update the release path
  for the struct device associated with an IOMMU. It freed the 'struct
  device', which was a pointer before, but is now embedded in another
  struct.

  Freeing from the middle of allocated memory had all kinds of nasty
  side effects when an IOMMU was unplugged. Unfortunatly nobody
  unplugged and IOMMU until now, so this was not discovered earlier. The
  fix is to make the 'struct device' a pointer again"

* tag 'iommu-fixes-v4.13-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu:
  iommu: Fix wrong freeing of iommu_device->dev

Pull char/misc fix from Greg KH:
 "Here is a single misc driver fix for 4.13-rc7. It resolves a reported
  problem in the Android binder driver due to previous patches in
  4.13-rc.

  It's been in linux-next with no reported issues"

* tag 'char-misc-4.13-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc:
  ANDROID: binder: fix proc->tsk check.

Pull staging/iio fixes from Greg KH:
 "Here are few small staging driver fixes, and some more IIO driver
  fixes for 4.13-rc7. Nothing major, just resolutions for some reported
  problems.

  All of these have been in linux-next with no reported problems"

* tag 'staging-4.13-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging:
  iio: magnetometer: st_magn: remove ihl property for LSM303AGR
  iio: magnetometer: st_magn: fix status register address for LSM303AGR
  iio: hid-sensor-trigger: Fix the race with user space powering up sensors
  iio: trigger: stm32-timer: fix get trigger mode
  iio: imu: adis16480: Fix acceleration scale factor for adis16480
  PATCH] iio: Fix some documentation warnings
  staging: rtl8188eu: add RNX-N150NUB support
  Revert "staging: fsl-mc: be consistent when checking strcmp() return"
  iio: adc: stm32: fix common clock rate
  iio: adc: ina219: Avoid underflow for sleeping time
  iio: trigger: stm32-timer: add enable attribute
  iio: trigger: stm32-timer: fix get/set down count direction
  iio: trigger: stm32-timer: fix write_raw return value
  iio: trigger: stm32-timer: fix quadrature mode get routine
  iio: bmp280: properly initialize device for humidity reading

Pull NTB fixes from Jon Mason:
 "NTB bug fixes to address an incorrect ntb_mw_count reference in the
  NTB transport, improperly bringing down the link if SPADs are
  corrupted, and an out-of-order issue regarding link negotiation and
  data passing"

* tag 'ntb-4.13-bugfixes' of git://github.com/jonmason/ntb:
  ntb: ntb_test: ensure the link is up before trying to configure the mws
  ntb: transport shouldn't disable link due to bogus values in SPADs
  ntb: use correct mw_count function in ntb_tool and ntb_transport

The "lock_page_killable()" function waits for exclusive access to the
page lock bit using the WQ_FLAG_EXCLUSIVE bit in the waitqueue entry
set.

That means that if it gets woken up, other waiters may have been
skipped.

That, in turn, means that if it sees the page being unlocked, it *must*
take that lock and return success, even if a lethal signal is also
pending.

So instead of checking for lethal signals first, we need to check for
them after we've checked the actual bit that we were waiting for.  Even
if that might then delay the killing of the process.

This matches the order of the old "wait_on_bit_lock()" infrastructure
that the page locking used to use (and is still used in a few other
areas).

Note that if we still return an error after having unsuccessfully tried
to acquire the page lock, that is ok: that means that some other thread
was able to get ahead of us and lock the page, and when that other
thread then unlocks the page, the wakeup event will be repeated.  So any
other pending waiters will now get properly woken up.

Fixes: 62906027 ("mm: add PageWaiters indicating tasks are waiting for a page bit")
Cc: Nick Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Jan Kara <jack@suse.cz>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Tim Chen and Kan Liang have been battling a customer load that shows
extremely long page wakeup lists.  The cause seems to be constant NUMA
migration of a hot page that is shared across a lot of threads, but the
actual root cause for the exact behavior has not been found.

Tim has a patch that batches the wait list traversal at wakeup time, so
that we at least don't get long uninterruptible cases where we traverse
and wake up thousands of processes and get nasty latency spikes.  That
is likely 4.14 material, but we're still discussing the page waitqueue
specific parts of it.

In the meantime, I've tried to look at making the page wait queues less
expensive, and failing miserably.  If you have thousands of threads
waiting for the same page, it will be painful.  We'll need to try to
figure out the NUMA balancing issue some day, in addition to avoiding
the excessive spinlock hold times.

That said, having tried to rewrite the page wait queues, I can at least
fix up some of the braindamage in the current situation. In particular:

 (a) we don't want to continue walking the page wait list if the bit
     we're waiting for already got set again (which seems to be one of
     the patterns of the bad load).  That makes no progress and just
     causes pointless cache pollution chasing the pointers.

 (b) we don't want to put the non-locking waiters always on the front of
     the queue, and the locking waiters always on the back.  Not only is
     that unfair, it means that we wake up thousands of reading threads
     that will just end up being blocked by the writer later anyway.

Also add a comment about the layout of 'struct wait_page_key' - there is
an external user of it in the cachefiles code that means that it has to
match the layout of 'struct wait_bit_key' in the two first members.  It
so happens to match, because 'struct page *' and 'unsigned long *' end
up having the same values simply because the page flags are the first
member in struct page.

Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Christopher Lameter <cl@linux.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>