Pull locking fixes from Borislav Petkov:
 "Two fixes from the locking/urgent pile:

   - Fix lockdep's detection of "USED" <- "IN-NMI" inversions (Peter
     Zijlstra)

   - Make percpu-rwsem operations on the semaphore's ->read_count
     IRQ-safe because it can be used in an IRQ context (Hou Tao)"

* tag 'locking_urgent_for_v5.9_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/percpu-rwsem: Use this_cpu_{inc,dec}() for read_count
  locking/lockdep: Fix "USED" <- "IN-NMI" inversions

Pull libnvdimm fixes from Dan Williams:
 "A handful of fixes to address a string of mistakes in the mechanism
  for device-mapper to determine if its component devices are dax
  capable.

   - Fix an original bug in device-mapper table reference counting when
     interrogating dax capability in the component device. This bug was
     hidden by the following bug.

   - Fix device-mapper to use the proper helper (dax_supported() instead
     of the leaf helper generic_fsdax_supported()) to determine dax
     operation of a stacked block device configuration. The original
     implementation is only valid for one level of dax-capable block
     device stacking. This bug was discovered while fixing the below
     regression.

   - Fix an infinite recursion regression introduced by broken attempts
     to quiet the generic_fsdax_supported() path and make it bail out
     before logging "dax capability not found" errors"

* tag 'libnvdimm-fixes-5.9-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm:
  dax: Fix stack overflow when mounting fsdax pmem device
  dm: Call proper helper to determine dax support
  dm/dax: Fix table reference counts

Pull tty/serial/fbcon fixes from Greg KH:
 "Here are some small tty/serial and one more fbcon fix.

  They include:

   - serial core locking regression fixes

   - new device ids for 8250_pci driver

   - fbcon fix for syzbot found issue

  All have been in linux-next with no reported issues"

* tag 'tty-5.9-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty:
  fbcon: Fix user font detection test at fbcon_resize().
  serial: 8250_pci: Add Realtek 816a and 816b
  serial: core: fix console port-lock regression
  serial: core: fix port-lock initialisation

DM was calling generic_fsdax_supported() to determine whether a device
referenced in the DM table supports DAX. However this is a helper for "leaf" device drivers so that
they don't have to duplicate common generic checks. High level code
should call dax_supported() helper which that calls into appropriate
helper for the particular device. This problem manifested itself as
kernel messages:

dm-3: error: dax access failed (-95)

when lvm2-testsuite run in cases where a DM device was stacked on top of
another DM device.

Fixes: 7bf7eac8d648 ("dax: Arrange for dax_supported check to span multiple devices")
Cc: <stable@vger.kernel.org>
Tested-by: Adrian Huang <ahuang12@lenovo.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/160061715195.13131.5503173247632041975.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Commit 32927393dc1c ("sysctl: pass kernel pointers to ->proc_handler")
changed ctl_table.proc_handler to take a kernel pointer.  Adjust the
signature of stack_erasing_sysctl to match ctl_table.proc_handler which
fixes the following sparse warning:

kernel/stackleak.c:31:50: warning: incorrect type in argument 3 (different address spaces)
kernel/stackleak.c:31:50:    expected void *
kernel/stackleak.c:31:50:    got void [noderef] __user *buffer

Fixes: 32927393dc1c ("sysctl: pass kernel pointers to ->proc_handler")
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lkml.kernel.org/r/20200907093253.13656-1-tklauser@distanz.ch
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Commit 32927393dc1c ("sysctl: pass kernel pointers to ->proc_handler")
changed ctl_table.proc_handler to take a kernel pointer.  Adjust the
signature of ftrace_enable_sysctl to match ctl_table.proc_handler which
fixes the following sparse warning:

kernel/trace/ftrace.c:7544:43: warning: incorrect type in argument 3 (different address spaces)
kernel/trace/ftrace.c:7544:43:    expected void *
kernel/trace/ftrace.c:7544:43:    got void [noderef] __user *buffer

Fixes: 32927393dc1c ("sysctl: pass kernel pointers to ->proc_handler")
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lkml.kernel.org/r/20200907093207.13540-1-tklauser@distanz.ch
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Pull arm64 fixes from Catalin Marinas:

 - Allow CPUs affected by erratum 1418040 to come online late
   (previously we only fixed the other case - CPUs not affected by the
   erratum coming up late).

 - Fix branch offset in BPF JIT.

 - Defer the stolen time initialisation to the CPU online time from the
   CPU starting time to avoid a (sleep-able) memory allocation in an
   atomic context.

* tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux:
  arm64: paravirt: Initialize steal time when cpu is online
  arm64: bpf: Fix branch offset in JIT
  arm64: Allow CPUs unffected by ARM erratum 1418040 to come in late

Pull power management updates from Rafael Wysocki:
 "These add a new CPU ID to the RAPL power capping driver and prevent
  the ACPI processor idle driver from triggering RCU-lockdep complaints.

  Specifics:

   - Add support for the Lakefield chip to the RAPL power capping driver
     (Ricardo Neri).

   - Modify the ACPI processor idle driver to prevent it from triggering
     RCU-lockdep complaints which has started to happen after recent
     changes in that area (Peter Zijlstra)"

* tag 'pm-5.9-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  ACPI: processor: Take over RCU-idle for C3-BM idle
  cpuidle: Allow cpuidle drivers to take over RCU-idle
  ACPI: processor: Use CPUIDLE_FLAG_TLB_FLUSHED
  ACPI: processor: Use CPUIDLE_FLAG_TIMER_STOP
  powercap: RAPL: Add support for Lakefield

Pull sound fixes from Takashi Iwai:
 "Here is a collection of fixes for 5.9. All look small and are nothing
  scary.

  The majority of changes are about ASoC driver- specific fixes, while
  there are a couple of ASoC core fixes (DAI lookup and lockdep stuff)
  and usual HD-audio quirks"

* tag 'sound-5.9-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound: (23 commits)
  ALSA: hda/realtek - The Mic on a RedmiBook doesn't work
  ASoC: tlv320adcx140: Wake up codec before accessing register
  ASoC: core: Do not cleanup uninitialized dais on soc_pcm_open failure
  ALSA: hda: fixup headset for ASUS GX502 laptop
  ASoC: Intel: bytcr_rt5640: Add quirk for MPMAN Converter9 2-in-1
  ASoC: Intel: haswell: Fix power transition refactor
  ASoC: tlv320adcx140: Fix accessing uninitialized adcx140->dev
  ASoC: wm8994: Ensure the device is resumed in wm89xx_mic_detect functions
  ASoC: wm8994: Skip setting of the WM8994_MICBIAS register for WM1811
  ASoC: meson: axg-toddr: fix channel order on g12 platforms
  ASoC: soc-core: add snd_soc_find_dai_with_mutex()
  ASoC: qcom: common: Fix refcount imbalance on error
  ASoC: rt700: Fix return check for devm_regmap_init_sdw()
  ASoC: rt715: Fix return check for devm_regmap_init_sdw()
  ASoC: rt711: Fix return check for devm_regmap_init_sdw()
  ASoC: rt1308-sdw: Fix return check for devm_regmap_init_sdw()
  ASoC: max98373: Fix return check for devm_regmap_init_sdw()
  ASoC: ti: fixup ams_delta_mute() function name
  ASoC: pcm3168a: ignore 0 Hz settings
  ASoC: Intel: tgl_max98373: fix a runtime pm issue in multi-thread case
  ...

Commit 2a9127fcf229 ("mm: rewrite wait_on_page_bit_common() logic") made
the page locking entirely fair, in that if a waiter came in while the
lock was held, the lock would be transferred to the lockers strictly in
order.

That was intended to finally get rid of the long-reported watchdog
failures that involved the page lock under extreme load, where a process
could end up waiting essentially forever, as other page lockers stole
the lock from under it.

It also improved some benchmarks, but it ended up causing huge
performance regressions on others, simply because fair lock behavior
doesn't end up giving out the lock as aggressively, causing better
worst-case latency, but potentially much worse average latencies and
throughput.

Instead of reverting that change entirely, this introduces a controlled
amount of unfairness, with a sysctl knob to tune it if somebody needs
to.  But the default value should hopefully be good for any normal load,
allowing a few rounds of lock stealing, but enforcing the strict
ordering before the lock has been stolen too many times.

There is also a hint from Matthieu Baerts that the fair page coloring
may end up exposing an ABBA deadlock that is hidden by the usual
optimistic lock stealing, and while the unfairness doesn't fix the
fundamental issue (and I'm still looking at that), it avoids it in
practice.

The amount of unfairness can be modified by writing a new value to the
'sysctl_page_lock_unfairness' variable (default value of 5, exposed
through /proc/sys/vm/page_lock_unfairness), but that is hopefully
something we'd use mainly for debugging rather than being necessary for
any deep system tuning.

This whole issue has exposed just how critical the page lock can be, and
how contended it gets under certain locks.  And the main contention
doesn't really seem to be anything related to IO (which was the origin
of this lock), but for things like just verifying that the page file
mapping is stable while faulting in the page into a page table.

Link: https://lore.kernel.org/linux-fsdevel/ed8442fd-6f54-dd84-cd4a-941e8b7ee603@MichaelLarabel.com/
Link: https://www.phoronix.com/scan.php?page=article&item=linux-50-59&num=1
Link: https://lore.kernel.org/linux-fsdevel/c560a38d-8313-51fb-b1ec-e904bd8836bc@tessares.net/
Reported-and-tested-by: Michael Larabel <Michael@michaellarabel.com>
Tested-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Chris Mason <clm@fb.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>