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Peter Zijlstra 279b5165ff perf/core: Remove confusing comment and move put_ctx() 
Since commit:

  321027c1fe ("perf/core: Fix concurrent sys_perf_event_open() vs. 'move_group' race")

... the code looks like (assuming move_group==1):

  gctx = __perf_event_ctx_lock_double(group_leader, ctx);

  perf_remove_from_context(group_leader, 0);
  list_for_each_entry(sibling, &group_leader->sibling_list, group_entry) {
	perf_remove_from_context(sibling, 0);
	put_ctx(gctx);
  }

  /* ... */

  /* misleading comment about how this is the last reference */
  put_ctx(gctx);

  perf_event_ctx_unlock(group_leader, gctx);

What that 'last' put_ctx() does is drop @group_leader's reference on
gctx after having dropped all its potential sibling references.

But the thing is that __perf_event_ctx_lock_double() returns with a
reference _and_ a held lock, and perf_event_ctx_unlock() unlocks that
lock and drops that reference. Therefore that put_ctx() cannot be the
'last' of anything, nor is there an unbalance in puts.

To reduce confusion, remove the comment and place the put_ctx() next
to the remove_from_context() call.

Reported-by: Ben Hutchings <ben@decadent.org.uk>
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: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 		2017-02-24 08:56:32 +01:00
Documentation ACPI updates for v4.11-rc1 2017-02-20 17:55:15 -08:00
arch ACPI updates for v4.11-rc1 2017-02-20 17:55:15 -08:00
block cfq-iosched: don't call wbt_disable_default() with IRQs disabled 2017-02-16 08:02:06 -07:00
certs certs: Add a secondary system keyring that can be added to dynamically 2016-04-11 22:48:09 +01:00
crypto crypto: algif_aead - Fix kernel panic on list_del 2017-02-03 17:45:48 +08:00
drivers Generic device properties framework updates for v4.11-rc1 2017-02-20 18:06:09 -08:00
firmware WHENCE: use https://linuxtv.org for LinuxTV URLs 2015-12-04 10:35:11 -02:00
fs Merge branch 'for-next' of git://git.samba.org/sfrench/cifs-2.6 2017-02-20 18:38:47 -08:00
include For this cycle we add support for the shutdown ioctl, which is 2017-02-20 18:24:39 -08:00
init 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
ipc ipc/sem.c: fix incorrect sem_lock pairing 2017-01-10 18:31:55 -08:00
kernel perf/core: Remove confusing comment and move put_ctx() 2017-02-24 08:56:32 +01:00
lib For this cycle we add support for the shutdown ioctl, which is 2017-02-20 18:24:39 -08:00
mm mm/slub.c: fix random_seq offset destruction 2017-02-08 15:41:43 -08:00
net 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
samples Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-02-20 12:21:13 -08:00
scripts Merge branch 'pm-tools' 2017-02-20 14:26:34 +01:00
security 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
sound ALSA: hda - adding a new NV HDMI/DP codec ID in the driver 2017-02-09 08:57:47 +01:00
tools perf/core improvements and fixes: 2017-02-21 09:05:29 +01:00
usr kbuild: initramfs cleanup, set target from Kconfig 2017-01-05 09:40:16 -08:00
virt KVM/ARM updates for 4.10-rc4 2017-01-17 15:04:59 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
…
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Merge branch 'misc' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild 2016-08-02 16:48:52 -04:00
.mailmap mailmap: add codeaurora.org names for nameless email commits 2017-01-10 18:31:55 -08:00
COPYING
…
CREDITS MAINTAINERS: Remove old e-mail address 2017-02-13 12:24:56 -05:00
Kbuild scripts/gdb: provide linux constants 2016-05-23 17:04:14 -07:00
Kconfig
…
MAINTAINERS Various cleanups for the file system encryption feature. 2017-02-20 18:22:31 -08:00
Makefile Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-02-20 12:21:13 -08:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.