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Revision 9107c89e269d2738019861bb518e3d59bef01781 authored by Peter Zijlstra on 24 February 2016, 17:45:45 UTC, committed by Ingo Molnar on 25 February 2016, 07:42:34 UTC 
perf: Fix race between event install and jump_labels
 
perf_install_in_context() relies upon the context switch hooks to have
scheduled in events when the IPI misses its target -- after all, if
the task has moved from the CPU (or wasn't running at all), it will
have to context switch to run elsewhere.

This however doesn't appear to be happening.

It is possible for the IPI to not happen (task wasn't running) only to
later observe the task running with an inactive context.

The only possible explanation is that the context switch hooks are not
called. Therefore put in a sync_sched() after toggling the jump_label
to guarantee all CPUs will have them enabled before we install an
event.

A simple if (0->1) sync_sched() will not in fact work, because any
further increment can race and complete before the sync_sched().
Therefore we must jump through some hoops.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dvyukov@google.com
Cc: eranian@google.com
Cc: oleg@redhat.com
Cc: panand@redhat.com
Cc: sasha.levin@oracle.com
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/20160224174947.980211985@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
1 parent a69b0ca
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Makefile 
#
# This file is subject to the terms and conditions of the GNU General Public
# License.  See the file "COPYING" in the main directory of this archive
# for more details.
#
# Copyright (C) 2004-2006 Atmel Corporation.

# Default target when executing plain make
.PHONY: all
all: uImage vmlinux.elf

KBUILD_DEFCONFIG	:= atstk1002_defconfig

KBUILD_CFLAGS	+= -pipe -fno-builtin -mno-pic -D__linux__
KBUILD_AFLAGS	+= -mrelax -mno-pic
KBUILD_CFLAGS_MODULE += -mno-relax
LDFLAGS_vmlinux	+= --relax

cpuflags-$(CONFIG_PLATFORM_AT32AP)	+= -march=ap

KBUILD_CFLAGS	+= $(cpuflags-y)
KBUILD_AFLAGS	+= $(cpuflags-y)

CHECKFLAGS	+= -D__avr32__ -D__BIG_ENDIAN

machine-$(CONFIG_PLATFORM_AT32AP) := at32ap
machdirs	:= $(patsubst %,arch/avr32/mach-%/, $(machine-y))

KBUILD_CPPFLAGS	+= $(patsubst %,-I$(srctree)/%include,$(machdirs))

head-$(CONFIG_LOADER_U_BOOT)		+= arch/avr32/boot/u-boot/head.o
head-y					+= arch/avr32/kernel/head.o
core-y					+= $(machdirs)
core-$(CONFIG_BOARD_ATSTK1000)		+= arch/avr32/boards/atstk1000/
core-$(CONFIG_BOARD_ATNGW100_COMMON)	+= arch/avr32/boards/atngw100/
core-$(CONFIG_BOARD_HAMMERHEAD)		+= arch/avr32/boards/hammerhead/
core-$(CONFIG_BOARD_FAVR_32)		+= arch/avr32/boards/favr-32/
core-$(CONFIG_BOARD_MERISC)		+= arch/avr32/boards/merisc/
core-$(CONFIG_BOARD_MIMC200)		+= arch/avr32/boards/mimc200/
core-$(CONFIG_LOADER_U_BOOT)		+= arch/avr32/boot/u-boot/
core-y					+= arch/avr32/kernel/
core-y					+= arch/avr32/mm/
drivers-$(CONFIG_OPROFILE)		+= arch/avr32/oprofile/
libs-y					+= arch/avr32/lib/

BOOT_TARGETS := vmlinux.elf vmlinux.bin uImage uImage.srec

.PHONY: $(BOOT_TARGETS) install

boot := arch/$(ARCH)/boot/images

             KBUILD_IMAGE := $(boot)/uImage
vmlinux.elf: KBUILD_IMAGE := $(boot)/vmlinux.elf
vmlinux.cso: KBUILD_IMAGE := $(boot)/vmlinux.cso
uImage.srec: KBUILD_IMAGE := $(boot)/uImage.srec
uImage:      KBUILD_IMAGE := $(boot)/uImage

quiet_cmd_listing = LST     $@
      cmd_listing = avr32-linux-objdump $(OBJDUMPFLAGS) -lS $< > $@
quiet_cmd_disasm  = DIS     $@
      cmd_disasm  = avr32-linux-objdump $(OBJDUMPFLAGS) -d $< > $@

vmlinux.elf vmlinux.bin uImage.srec uImage vmlinux.cso: vmlinux
	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@

install: vmlinux
	$(Q)$(MAKE) $(build)=$(boot) BOOTIMAGE=$(KBUILD_IMAGE) $@

vmlinux.s: vmlinux
	$(call if_changed,disasm)

vmlinux.lst: vmlinux
	$(call if_changed,listing)

CLEAN_FILES += vmlinux.s vmlinux.lst

archclean:
	$(Q)$(MAKE) $(clean)=$(boot)

define archhelp
  @echo '* vmlinux.elf		- ELF image with load address 0'
  @echo '  vmlinux.cso		- PathFinder CSO image'
  @echo '* uImage		- Create a bootable image for U-Boot'
endef
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