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Peter Zijlstra d8a8cfc769 perf/core: Better explain the inherit magic 
While going through the event inheritance code Oleg got confused.

Add some comments to better explain the silent dissapearance of
orphaned events.

So what happens is that at perf_event_release_kernel() time; when an
event looses its connection to userspace (and ceases to exist from the
user's perspective) we can still have an arbitrary amount of inherited
copies of the event. We want to synchronously find and remove all
these child events.

Since that requires a bit of lock juggling, there is the possibility
that concurrent clone()s will create new child events. Therefore we
first mark the parent event as DEAD, which marks all the extant child
events as orphaned.

We then avoid copying orphaned events; in order to avoid getting more
of them.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: fweisbec@gmail.com
Link: http://lkml.kernel.org/r/20170316125823.289567442@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-03-16 14:16:53 +01:00
..
bpf bpf: fix spelling mistake: "proccessed" -> "processed" 2017-02-23 10:46:08 -05:00
cgroup Merge branch 'for-4.11' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2017-02-27 21:41:08 -08:00
configs config: android-base: enable hardened usercopy and kernel ASLR 2017-02-27 18:43:46 -08:00
debug kdb: call vkdb_printf() from vprintk_default() only when wanted 2016-12-14 16:04:08 -08:00
events perf/core: Better explain the inherit magic 2017-03-16 14:16:53 +01:00
gcov
irq scripts/spelling.txt: add "an user" pattern and fix typo instances 2017-02-27 18:43:46 -08:00
livepatch
locking Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-02-20 13:23:30 -08:00
power This renames the (now inaccurate) CONFIG_DEBUG_RODATA and related config 2017-02-21 17:56:45 -08:00
printk Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk 2017-02-22 17:33:34 -08:00
rcu Merge branches 'doc.2017.01.15b', 'dyntick.2017.01.23a', 'fixes.2017.01.23a', 'srcu.2017.01.25a' and 'torture.2017.01.15b' into HEAD 2017-01-25 12:56:05 -08:00
sched Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-02-28 11:44:01 -08:00
time Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-02-20 12:52:55 -08:00
trace perf/core: Rename CONFIG_[UK]PROBE_EVENT to CONFIG_[UK]PROBE_EVENTS 2017-03-01 10:26:39 +01:00
.gitignore
acct.c acct: Convert obsolete cputime type to nsecs 2017-02-01 09:13:51 +01:00
async.c
audit.c Merge branch 'stable-4.11' of git://git.infradead.org/users/pcmoore/audit 2017-02-21 13:25:50 -08:00
audit.h Merge branch 'stable-4.11' of git://git.infradead.org/users/pcmoore/audit 2017-02-21 13:25:50 -08:00
audit_fsnotify.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2016-12-17 18:44:00 -08:00
audit_tree.c Merge branch 'stable-4.10' of git://git.infradead.org/users/pcmoore/audit 2017-01-05 23:06:06 -08:00
audit_watch.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2016-12-17 18:44:00 -08:00
auditfilter.c audit: add support for session ID user filter 2016-11-29 15:10:12 -05:00
auditsc.c Merge branch 'stable-4.11' of git://git.infradead.org/users/pcmoore/audit 2017-02-21 13:25:50 -08:00
backtracetest.c
bounds.c
capability.c capability: export has_capability 2017-01-12 07:01:56 -07:00
compat.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
configs.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
context_tracking.c
cpu.c cpu/hotplug: Remove unused but set variable in _cpu_down() 2017-01-18 11:55:09 +01:00
cpu_pm.c
crash_dump.c
cred.c
delayacct.c delaycct: Convert obsolete cputime type to nsecs 2017-02-01 09:13:52 +01:00
dma.c
elfcore.c
exec_domain.c
exit.c mm: add new mmgrab() helper 2017-02-27 18:43:48 -08:00
extable.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2017-02-22 10:15:09 -08:00
fork.c mm: add new mmget() helper 2017-02-27 18:43:48 -08:00
freezer.c
futex.c mm: add new mmgrab() helper 2017-02-27 18:43:48 -08:00
futex_compat.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
groups.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
hung_task.c hung_task: decrement sysctl_hung_task_warnings only if it is positive 2016-12-12 18:55:09 -08:00
irq_work.c
jump_label.c This release has no new tracing features, just clean ups, minor fixes 2017-02-27 13:26:17 -08:00
kallsyms.c bpf: make jited programs visible in traces 2017-02-17 13:40:05 -05:00
kcmp.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt
kcov.c kcov: make kcov work properly with KASLR enabled 2016-12-20 09:48:47 -08:00
kexec.c
kexec_core.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk 2017-02-22 17:33:34 -08:00
kexec_file.c ima: on soft reboot, save the measurement list 2016-12-20 09:48:44 -08:00
kexec_internal.h kexec_file: Allow arch-specific memory walking for kexec_add_buffer 2016-11-30 23:14:57 +11:00
kmod.c Introduce STATIC_USERMODEHELPER to mediate call_usermodehelper() 2017-01-19 12:59:45 +01:00
kprobes.c powerpc updates for 4.11 part 1. 2017-02-22 10:30:38 -08:00
ksysfs.c kernel/ksysfs.c: add __ro_after_init to bin_attribute structure 2017-02-24 17:46:56 -08:00
kthread.c time: Remove CONFIG_TIMER_STATS 2017-02-10 11:15:08 +01:00
latencytop.c
Makefile cgroup: move cgroup files under kernel/cgroup/ 2016-12-27 14:49:05 -05:00
membarrier.c Fix: Disable sys_membarrier when nohz_full is enabled 2017-01-23 11:32:16 -08:00
memremap.c mm, devm_memremap_pages: hold device_hotplug lock over mem_hotplug_{begin, done} 2017-02-24 17:46:53 -08:00
module-internal.h
module.c Modules updates for v4.11 2017-02-22 17:08:33 -08:00
module_signing.c
notifier.c kernel/notifier.c: simplify expression 2017-02-24 17:46:56 -08:00
nsproxy.c
padata.c
panic.c sparc64: Send break twice from console to return to boot prom 2017-02-23 08:27:24 -08:00
params.c
pid.c locking/atomic, kref: Add KREF_INIT() 2017-01-14 11:37:18 +01:00
pid_namespace.c pid: fix lockdep deadlock warning due to ucount_lock 2017-01-10 13:34:56 +13:00
profile.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
ptrace.c ptrace: Don't allow accessing an undumpable mm 2016-11-22 12:57:38 -06:00
range.c
reboot.c
relay.c lib/vsprintf.c: remove %Z support 2017-02-27 18:43:47 -08:00
resource.c
seccomp.c seccomp: Only dump core when single-threaded 2017-02-23 09:42:35 +11:00
signal.c sigaltstack: support SS_AUTODISARM for CONFIG_COMPAT 2017-02-27 18:43:45 -08:00
smp.c
smpboot.c
smpboot.h
softirq.c
stacktrace.c stacktrace, lockdep: Fix address, newline ugliness 2017-02-08 08:21:31 +01:00
stop_machine.c locking/core, stop_machine: Yield the CPU during stop machine() 2016-11-16 10:15:09 +01:00
sys.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2017-02-23 20:33:51 -08:00
sys_ni.c move aio compat to fs/aio.c 2016-12-22 22:58:37 -05:00
sysctl.c sched/rt: Show the 'sched_rr_timeslice' SCHED_RR timeslice tuning knob in milliseconds 2017-02-01 11:01:30 +01:00
sysctl_binary.c sysctl: add KERN_CONT to deprecated_sysctl_warning() 2016-12-14 16:04:07 -08:00
task_work.c
taskstats.c
test_kprobes.c
torture.c scripts/spelling.txt: add "varible" pattern and fix typo instances 2017-02-27 18:43:47 -08:00
tracepoint.c tracing: Have the reg function allow to fail 2016-12-09 09:13:30 -05:00
tsacct.c tsacct: Convert obsolete cputime type to nsecs 2017-02-01 09:13:52 +01:00
ucount.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2017-02-23 20:33:51 -08:00
uid16.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
up.c
user-return-notifier.c
user.c
user_namespace.c
utsname.c
utsname_sysctl.c
watchdog.c kernel/watchdog: prevent false hardlockup on overloaded system 2017-01-24 16:26:14 -08:00
watchdog_hld.c kernel/watchdog.c: do not hardcode CPU 0 as the initial thread 2017-02-22 16:41:27 -08:00
workqueue.c time: Remove CONFIG_TIMER_STATS 2017-02-10 11:15:08 +01:00
workqueue_internal.h