Commit 12ca6ad2 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: default avatarSasha Levin <sasha.levin@oracle.com>
Tested-by: default avatarSasha Levin <sasha.levin@oracle.com>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent c1274499

kernel/events/core.c

+1 −19
Original line number Diff line number Diff line
@@ -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) { }

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