[3.16.y-ckt stable] Patch "perf: Fix events installation during moving group" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    perf: Fix events installation during moving group

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt4.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 3a77fe0b61d44262d0ba760607da69e20b53e6de Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa at kernel.org>
Date: Wed, 10 Dec 2014 21:23:51 +0100
Subject: perf: Fix events installation during moving group

commit 9fc81d87420d0d3fd62d5e5529972c0ad9eab9cc upstream.

We allow PMU driver to change the cpu on which the event
should be installed to. This happened in patch:

  e2d37cd213dc ("perf: Allow the PMU driver to choose the CPU on which to install events")

This patch also forces all the group members to follow
the currently opened events cpu if the group happened
to be moved.

This and the change of event->cpu in perf_install_in_context()
function introduced in:

  0cda4c023132 ("perf: Introduce perf_pmu_migrate_context()")

forces group members to change their event->cpu,
if the currently-opened-event's PMU changed the cpu
and there is a group move.

Above behaviour causes problem for breakpoint events,
which uses event->cpu to touch cpu specific data for
breakpoints accounting. By changing event->cpu, some
breakpoints slots were wrongly accounted for given
cpu.

Vinces's perf fuzzer hit this issue and caused following
WARN on my setup:

   WARNING: CPU: 0 PID: 20214 at arch/x86/kernel/hw_breakpoint.c:119 arch_install_hw_breakpoint+0x142/0x150()
   Can't find any breakpoint slot
   [...]

This patch changes the group moving code to keep the event's
original cpu.

Reported-by: Vince Weaver <vince at deater.net>
Signed-off-by: Jiri Olsa <jolsa at redhat.com>
Cc: Arnaldo Carvalho de Melo <acme at redhat.com>
Cc: Frederic Weisbecker <fweisbec at gmail.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Stephane Eranian <eranian at google.com>
Cc: Vince Weaver <vince at deater.net>
Cc: Yan, Zheng <zheng.z.yan at intel.com>
Link: http://lkml.kernel.org/r/1418243031-20367-3-git-send-email-jolsa@kernel.org
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/events/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6bc75223aaa7..cfaeffaefc75 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7329,11 +7329,11 @@ SYSCALL_DEFINE5(perf_event_open,

 	if (move_group) {
 		synchronize_rcu();
-		perf_install_in_context(ctx, group_leader, event->cpu);
+		perf_install_in_context(ctx, group_leader, group_leader->cpu);
 		get_ctx(ctx);
 		list_for_each_entry(sibling, &group_leader->sibling_list,
 				    group_entry) {
-			perf_install_in_context(ctx, sibling, event->cpu);
+			perf_install_in_context(ctx, sibling, sibling->cpu);
 			get_ctx(ctx);
 		}
 	}
--
2.1.4