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Message-ID: <lsq.1487198501.361211593@decadent.org.uk>
Date: Wed, 15 Feb 2017 22:41:41 +0000
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC: akpm@...ux-foundation.org, "Ingo Molnar" <mingo@...nel.org>,
"Stephane Eranian" <eranian@...gle.com>,
"Linus Torvalds" <torvalds@...ux-foundation.org>,
"Arnaldo Carvalho de Melo" <acme@...hat.com>,
"Vince Weaver" <vincent.weaver@...ne.edu>,
"Sasha Levin" <sasha.levin@...cle.com>,
"Peter Zijlstra" <peterz@...radead.org>,
"Jiri Olsa" <jolsa@...hat.com>,
"Thomas Gleixner" <tglx@...utronix.de>,
"Frederic Weisbecker" <fweisbec@...il.com>
Subject: [PATCH 3.16 287/306] perf: Fix race in swevent hash
3.16.40-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Peter Zijlstra <peterz@...radead.org>
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@...cle.com>
Tested-by: Sasha Levin <sasha.levin@...cle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
kernel/events/core.c | 20 +-------------------
1 file changed, 1 insertion(+), 19 deletions(-)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5595,9 +5595,6 @@ 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);
@@ -5844,14 +5841,8 @@ 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);
@@ -5918,7 +5909,6 @@ 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;
@@ -8050,7 +8040,6 @@ 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;
@@ -8103,14 +8092,7 @@ 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) { }
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