This is a note to let you know that I've just added the patch titled
perf: Fix race in swevent hash
to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-fix-race-in-swevent-hash.patch
and it can be found in the queue-3.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 12ca6ad2e3a896256f086497a7c7406a547ee373 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Tue, 15 Dec 2015 13:49:05 +0100
Subject: perf: Fix race in swevent hash
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
commit 12ca6ad2e3a896256f086497a7c7406a547ee373 upstream.
There's a race on CPU unplug where we free the swevent hash array
while it can still have events on. This will result in a
use-after-free which is BAD.
Simply do not free the hash array on unplug. This leaves the thing
around and no use-after-free takes place.
When the last swevent dies, we do a for_each_possible_cpu() iteration
anyway to clean these up, at which time we'll free it, so no leakage
will occur.
Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Amit Pundir <amit.pundir@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/events/core.c | 20 +-------------------
1 file changed, 1 insertion(+), 19 deletions(-)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5851,9 +5851,6 @@ struct swevent_htable {
/* Recursion avoidance in each contexts */
int recursion[PERF_NR_CONTEXTS];
-
- /* Keeps track of cpu being initialized/exited */
- bool online;
};
static DEFINE_PER_CPU(struct swevent_htable, swevent_htable);
@@ -6111,14 +6108,8 @@ static int perf_swevent_add(struct perf_
hwc->state = !(flags & PERF_EF_START);
head = find_swevent_head(swhash, event);
- if (!head) {
- /*
- * We can race with cpu hotplug code. Do not
- * WARN if the cpu just got unplugged.
- */
- WARN_ON_ONCE(swhash->online);
+ if (WARN_ON_ONCE(!head))
return -EINVAL;
- }
hlist_add_head_rcu(&event->hlist_entry, head);
@@ -6185,7 +6176,6 @@ static int swevent_hlist_get_cpu(struct
int err = 0;
mutex_lock(&swhash->hlist_mutex);
-
if (!swevent_hlist_deref(swhash) && cpu_online(cpu)) {
struct swevent_hlist *hlist;
@@ -8342,7 +8332,6 @@ static void perf_event_init_cpu(int cpu)
struct swevent_htable *swhash = &per_cpu(swevent_htable, cpu);
mutex_lock(&swhash->hlist_mutex);
- swhash->online = true;
if (swhash->hlist_refcount > 0) {
struct swevent_hlist *hlist;
@@ -8395,14 +8384,7 @@ static void perf_event_exit_cpu_context(
static void perf_event_exit_cpu(int cpu)
{
- struct swevent_htable *swhash = &per_cpu(swevent_htable, cpu);
-
perf_event_exit_cpu_context(cpu);
-
- mutex_lock(&swhash->hlist_mutex);
- swhash->online = false;
- swevent_hlist_release(swhash);
- mutex_unlock(&swhash->hlist_mutex);
}
#else
static inline void perf_event_exit_cpu(int cpu) { }
Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are
queue-3.18/arm64-perf-reject-groups-spanning-multiple-hw-pmus.patch
queue-3.18/x86-boot-fix-bss-corruption-overwrite-bug-in-early-x86-kernel-startup.patch
queue-3.18/perf-fix-race-in-swevent-hash.patch
queue-3.18/perf-fix-event-ctx-locking.patch