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authorPeter Zijlstra <peterz@infradead.org>2015-12-15 13:49:05 +0100
committerIngo Molnar <mingo@kernel.org>2016-01-06 10:52:39 +0100
commit12ca6ad2e3a896256f086497a7c7406a547ee373 (patch)
tree96f15b0a7c6622da00161b2b66ac6fb78019cfbe
parentc127449944659543e5e2423002f08f0af98dba5c (diff)
perf: Fix race in swevent hash
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@oracle.com> Tested-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.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>
-rw-r--r--kernel/events/core.c20
1 files changed, 1 insertions, 19 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index fd7de04..0a791a2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6488,9 +6488,6 @@ 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);
@@ -6748,14 +6745,8 @@ static int perf_swevent_add(struct perf_event *event, int flags)
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);
perf_event_update_userpage(event);
@@ -6823,7 +6814,6 @@ static int swevent_hlist_get_cpu(struct perf_event *event, int cpu)
int err = 0;
mutex_lock(&swhash->hlist_mutex);
-
if (!swevent_hlist_deref(swhash) && cpu_online(cpu)) {
struct swevent_hlist *hlist;
@@ -9286,7 +9276,6 @@ 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;
@@ -9328,14 +9317,7 @@ static void perf_event_exit_cpu_context(int cpu)
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) { }