thp: avoid VM_BUG_ON page_count(page) false positives in __collapse_huge_page_copy

Some time ago Petr once reproduced a false positive VM_BUG_ON in
khugepaged while running the autonuma-benchmark on a large 8 node system.
All production kernels out there have DEBUG_VM=n so it was only noticeable
on self built kernels.  It's not easily reproducible even on the 8 nodes
system.

Use page_freeze_refs to prevent speculative pagecache lookups to
trigger the false positives, so we're still able to check the
page_count to be exact.

This patch removes the false positive and it has been tested for a
while and it's good idea to queue it for upstream too. It's not urgent
and probably not worth it for -stable, though it wouldn't hurt. On
smaller systems it's not reproducible AFIK.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Petr Holasek <pholasek@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Merge remote-tracking branch 'signal/for-next'

Conflicts:
arch/alpha/Kconfig
arch/arm/Kconfig
arch/arm/include/asm/thread_info.h
arch/c6x/Kconfig
arch/cris/include/asm/Kbuild
arch/h8300/include/asm/Kbuild
arch/m32r/include/asm/Kbuild
arch/m68k/Kconfig
arch/mn10300/Kconfig
arch/powerpc/Kconfig
arch/s390/Kconfig
arch/x86/Kconfig
arch/x86/kernel/process_32.c
arch/x86/kernel/signal.c
fs/exec.c

Merge remote-tracking branch 'ktest/for-next'

Merge remote-tracking branch 'userns/for-next'

Conflicts:
fs/ubifs/debug.c
init/Kconfig
kernel/audit.c
kernel/auditsc.c
security/integrity/ima/ima_policy.c

Merge remote-tracking branch 'pwm/for-next'

Merge remote-tracking branch 'dma-mapping/dma-mapping-next'

Conflicts:
Documentation/devicetree/bindings/ata/ahci-platform.txt
arch/arm/boot/dts/highbank.dts

Merge remote-tracking branch 'kvmtool/master'

Merge remote-tracking branch 'samsung/for-next'

Conflicts:
arch/arm/mach-exynos/Makefile.boot

Merge remote-tracking branch 'renesas/next'

Merge remote-tracking branch 'msm/for-next'

Conflicts:
arch/arm/mach-msm/board-dt-8660.c
arch/arm/mach-msm/board-dt-8960.c
arch/arm/mach-msm/common.h
arch/arm/mach-vt8500/include/mach/restart.h

Merge remote-tracking branch 'ixp4xx/next'

Conflicts:
arch/arm/mach-ixp4xx/common.c
arch/arm/mach-ixp4xx/include/mach/ixp4xx-regs.h

Merge remote-tracking branch 'ep93xx/ep93xx-for-next'

Merge remote-tracking branch 'arm-soc/for-next'

Conflicts:
Documentation/devicetree/bindings/usb/platform-uhci.txt
arch/arm/include/asm/timex.h
arch/arm/mach-davinci/davinci.h
arch/arm/mach-davinci/dm355.c
arch/arm/mach-davinci/dm365.c
arch/arm/mach-davinci/include/mach/da8xx.h
arch/arm/mach-imx/clk-imx51-imx53.c
arch/arm/mach-integrator/integrator_cp.c
arch/arm/mach-omap2/board-rx51-peripherals.c
arch/arm/mach-s3c64xx/mach-mini6410.c
arch/arm/mach-s3c64xx/mach-real6410.c
arch/arm/mach-shmobile/include/mach/common.h
arch/arm/mach-tegra/devices.c
arch/arm/mach-ux500/cpu-db8500.c
arch/arm/mach-vt8500/bv07.c
arch/arm/mach-vt8500/devices-vt8500.c
arch/arm/mach-vt8500/devices-wm8505.c
arch/arm/mach-vt8500/devices.c
arch/arm/mach-vt8500/devices.h
arch/arm/mach-vt8500/wm8505_7in.c
drivers/clocksource/Makefile
drivers/dma/mmp_tdma.c
drivers/i2c/busses/i2c-omap.c
drivers/input/keyboard/omap-keypad.c
drivers/mfd/db8500-prcmu.c
drivers/mmc/host/davinci_mmc.c
drivers/mmc/host/omap.c
drivers/mtd/nand/Kconfig
drivers/mtd/nand/bcm_umi_nand.c
drivers/mtd/nand/nand_bcm_umi.h
drivers/mtd/nand/orion_nand.c
drivers/pinctrl/Makefile
drivers/spi/spi-davinci.c
drivers/staging/tidspbridge/core/wdt.c
drivers/usb/host/Kconfig
drivers/video/msm/mddi.c
drivers/video/msm/mdp.c
drivers/video/msm/mdp_hw.h
drivers/video/omap/lcd_ams_delta.c
drivers/video/omap2/dss/dispc.c
drivers/w1/masters/omap_hdq.c
sound/soc/omap/igep0020.c
sound/soc/omap/omap-mcbsp.c
sound/soc/omap/omap-pcm.c
sound/soc/omap/omap3beagle.c
sound/soc/omap/omap3evm.c
sound/soc/omap/overo.c

Merge remote-tracking branch 'gpio-lw/for-next'

Merge remote-tracking branch 'remoteproc/for-next'

Merge remote-tracking branch 'vhost/linux-next'

Conflicts:
drivers/net/tun.c

Merge remote-tracking branch 'pinctrl/for-next'

Merge remote-tracking branch 'writeback/writeback-for-next'

Merge remote-tracking branch 'tmem/linux-next'

Merge remote-tracking branch 'char-misc/char-misc-next'

Conflicts:
drivers/char/pcmcia/synclink_cs.c

Merge remote-tracking branch 'staging/staging-next'

Conflicts:
drivers/staging/Kconfig
drivers/staging/Makefile
drivers/staging/android/binder.c
drivers/staging/ipack/devices/ipoctal.c
drivers/staging/omap-thermal/omap-thermal-common.c
drivers/staging/serqt_usb2/serqt_usb2.c

Merge remote-tracking branch 'usb/usb-next'

Conflicts:
drivers/usb/core/usb-acpi.c
drivers/usb/serial/digi_acceleport.c
drivers/usb/serial/io_edgeport.c
drivers/usb/serial/io_ti.c
drivers/usb/serial/kl5kusb105.c
drivers/usb/serial/mos7720.c
drivers/usb/serial/mos7840.c

Merge remote-tracking branch 'tty/tty-next'

Conflicts:
drivers/tty/serial/omap-serial.c

Merge remote-tracking branch 'driver-core/driver-core-next'

Merge remote-tracking branch 'leds/for-next'

Merge remote-tracking branch 'regmap/for-next'

Merge remote-tracking branch 'drivers-x86/linux-next'

Merge remote-tracking branch 'workqueues/for-next'

Conflicts:
drivers/hid/hid-picolcd.c
drivers/isdn/mISDN/hwchannel.c
drivers/thermal/thermal_sys.c
drivers/video/omap2/displays/panel-taal.c

Merge remote-tracking branch 'xen-two/linux-next'

Merge remote-tracking branch 'kvm-ppc/kvm-ppc-next'

Merge remote-tracking branch 'kvm/linux-next'

Conflicts:
arch/s390/include/asm/processor.h
arch/x86/kvm/i8259.c

Merge remote-tracking branch 'kmemleak/kmemleak'

Merge remote-tracking branch 'tip/auto-latest'

Conflicts:
arch/Kconfig
arch/s390/Kconfig
arch/x86/Kconfig

Merge remote-tracking branch 'spi-mb/spi-next'

Merge remote-tracking branch 'dt-rh/for-next'

Merge remote-tracking branch 'edac-amd/for-next'

Conflicts:
Documentation/edac.txt
drivers/edac/amd64_edac.c

Merge remote-tracking branch 'edac/linux_next'

Merge remote-tracking branch 'fsnotify/for-next'

Conflicts:
kernel/audit_tree.c

Merge remote-tracking branch 'pm/linux-next'

Merge remote-tracking branch 'trivial/for-next'

Conflicts:
drivers/scsi/ipr.c
drivers/video/backlight/88pm860x_bl.c

Merge remote-tracking branch 'osd/linux-next'

Merge remote-tracking branch 'iommu/next'

Merge remote-tracking branch 'watchdog/master'

Merge remote-tracking branch 'selinux/master'

Merge remote-tracking branch 'security/next'

Merge remote-tracking branch 'regulator/for-next'

Conflicts:
Documentation/devicetree/bindings/regulator/tps6586x.txt

Merge remote-tracking branch 'omap_dss2/for-next'

Merge remote-tracking branch 'fbdev/fbdev-next'

Merge remote-tracking branch 'battery/master'

Conflicts:
include/linux/mfd/88pm860x.h

Merge remote-tracking branch 'mfd/for-next'

Conflicts:
Documentation/devicetree/bindings/regulator/tps6586x.txt
drivers/mfd/88pm860x-core.c
drivers/mfd/max8925-core.c
drivers/mfd/tc3589x.c
drivers/mfd/tps65217.c
drivers/regulator/anatop-regulator.c

Merge remote-tracking branch 'md/for-next'

Conflicts:
drivers/md/raid0.c
fs/bio.c

Merge remote-tracking branch 'slab/for-next'

Merge remote-tracking branch 'kgdb/kgdb-next'

Merge remote-tracking branch 'mmc/mmc-next'

Merge branch 'quilt/device-mapper'

Merge remote-tracking branch 'block/for-next'

Merge remote-tracking branch 'cgroup/for-next'

Merge remote-tracking branch 'input/next'

Merge branch 'quilt/rr'

Conflicts:
arch/xtensa/Kconfig

Merge remote-tracking branch 'sound-asoc/for-next'

Merge remote-tracking branch 'sound/for-next'

Conflicts:
arch/arm/mach-imx/mach-imx27_visstrim_m10.c

Merge remote-tracking branch 'drm/drm-next'

Conflicts:
drivers/gpu/drm/i915/i915_dma.c
drivers/gpu/drm/i915/intel_sdvo.c

Merge remote-tracking branch 'crypto/master'

Conflicts:
crypto/Kconfig

Merge remote-tracking branch 'l2-mtd/master'

Merge remote-tracking branch 'mtd/master'

Merge remote-tracking branch 'bluetooth/master'

Merge remote-tracking branch 'wireless-next/master'

Conflicts:
drivers/net/wireless/ath/ath9k/pci.c

Revert "be2net: fix vfs enumeration"

This reverts commit 51af6d7c1f31e0f3d42c87d53657ec7acb6e3462.

Merge remote-tracking branch 'net-next/master'

Conflicts:
drivers/net/team/team.c
drivers/net/usb/qmi_wwan.c
net/batman-adv/bat_iv_ogm.c
net/ipv4/fib_frontend.c
net/ipv4/route.c
net/l2tp/l2tp_netlink.c
net/socket.c

Merge remote-tracking branch 'slave-dma/next'

Merge remote-tracking branch 'target-updates/for-next'

Merge remote-tracking branch 'scsi/for-next'

Conflicts:
drivers/scsi/ipr.c
drivers/scsi/qla2xxx/qla_nx.c

Merge remote-tracking branch 'dlm/next'

Merge remote-tracking branch 'ubi/linux-next'

Merge remote-tracking branch 'ieee1394/for-next'

Merge remote-tracking branch 'thermal/next'

Merge remote-tracking branch 'cpuidle/cpuidle-next'

Conflicts:
drivers/cpuidle/coupled.c
include/linux/cpuidle.h

Merge remote-tracking branch 'acpi/next'

Merge remote-tracking branch 'pstore/master'

Merge remote-tracking branch 'infiniband/for-next'

Conflicts:
drivers/net/ethernet/mellanox/mlx4/mlx4.h

Merge remote-tracking branch 'libata/NEXT'

Merge remote-tracking branch 'kconfig/for-next'

Merge remote-tracking branch 'kbuild/for-next'

Merge remote-tracking branch 'v4l-dvb/master'

Conflicts:
arch/arm/mach-imx/mach-imx27_visstrim_m10.c

Merge remote-tracking branch 'hwmon-staging/hwmon-next'

Merge branch 'quilt/jdelvare-hwmon'

Merge remote-tracking branch 'i2c-embedded/i2c-embedded/for-next'

Merge branch 'quilt/i2c'

Merge remote-tracking branch 'hid/for-next'

Merge remote-tracking branch 'galak/next'

Merge remote-tracking branch 'powerpc/next'

Merge remote-tracking branch 'pci/next'

Merge remote-tracking branch 'vfs/for-next'

Merge remote-tracking branch 'xfs/for-next'

Merge remote-tracking branch 'ubifs/linux-next'

Merge remote-tracking branch 'v9fs/for-next'

Merge remote-tracking branch 'ocfs2/linux-next'

Merge remote-tracking branch 'nfsd/nfsd-next'

Merge remote-tracking branch 'nfs/linux-next'

Merge remote-tracking branch 'logfs/master'