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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
Raw File
Makefile 
#
# linux/arch/c6x/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.
#

KBUILD_DEFCONFIG := dsk6455_defconfig

cflags-y += -mno-dsbt -msdata=none -D__linux__

cflags-$(CONFIG_C6X_BIG_KERNEL) += -mlong-calls

CFLAGS_MODULE   += -mlong-calls -mno-dsbt -msdata=none

CHECKFLAGS      +=

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

ifdef CONFIG_CPU_BIG_ENDIAN
KBUILD_CFLAGS   += -mbig-endian
KBUILD_AFLAGS   += -mbig-endian
LINKFLAGS       += -mbig-endian
KBUILD_LDFLAGS  += -mbig-endian
LDFLAGS += -EB
endif

head-y          := arch/c6x/kernel/head.o
core-y          += arch/c6x/kernel/ arch/c6x/mm/ arch/c6x/platforms/
libs-y          += arch/c6x/lib/

# Default to vmlinux.bin, override when needed
all: vmlinux.bin

boot := arch/$(ARCH)/boot

# Are we making a dtbImage.<boardname> target? If so, crack out the boardname
DTB:=$(subst dtbImage.,,$(filter dtbImage.%, $(MAKECMDGOALS)))
export DTB

ifneq ($(DTB),)
core-y	+= $(boot)/dts/
endif

# With make 3.82 we cannot mix normal and wildcard targets

vmlinux.bin: vmlinux
	$(Q)$(MAKE) $(build)=$(boot) $(patsubst %,$(boot)/%,$@)

dtbImage.%: vmlinux
	$(Q)$(MAKE) $(build)=$(boot) $(patsubst %,$(boot)/%,$@)

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

define archhelp
  @echo '  vmlinux.bin     - Binary kernel image (arch/$(ARCH)/boot/vmlinux.bin)'
  @echo '  dtbImage.<dt>   - ELF image with $(arch)/boot/dts/<dt>.dts linked in'
  @echo '                  - stripped elf with fdt blob'
endef
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