perf: Fix crash in swevents

Frederic reported that because swevents handling doesn't disable IRQs
anymore, we can get a recursion of perf_adjust_period(), once from
overflow handling and once from the tick.

If both call ->disable, we get a double hlist_del_rcu() and trigger
a LIST_POISON2 dereference.

Since we don't actually need to stop/start a swevent to re-programm
the hardware (lack of hardware to program), simply nop out these
callbacks for the swevent pmu.

Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1275557609.27810.35218.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 858f56f..31d6afe 100644 (file)
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -4055,13 +4055,6 @@ static void perf_swevent_overflow(struct perf_event *event, u64 overflow,
        }
 }
 
-static void perf_swevent_unthrottle(struct perf_event *event)
-{
-       /*
-        * Nothing to do, we already reset hwc->interrupts.
-        */
-}
-
 static void perf_swevent_add(struct perf_event *event, u64 nr,
                               int nmi, struct perf_sample_data *data,
                               struct pt_regs *regs)
@@ -4276,11 +4269,22 @@ static void perf_swevent_disable(struct perf_event *event)
        hlist_del_rcu(&event->hlist_entry);
 }
 
+static void perf_swevent_void(struct perf_event *event)
+{
+}
+
+static int perf_swevent_int(struct perf_event *event)
+{
+       return 0;
+}
+
 static const struct pmu perf_ops_generic = {
        .enable         = perf_swevent_enable,
        .disable        = perf_swevent_disable,
+       .start          = perf_swevent_int,
+       .stop           = perf_swevent_void,
        .read           = perf_swevent_read,
-       .unthrottle     = perf_swevent_unthrottle,
+       .unthrottle     = perf_swevent_void, /* hwc->interrupts already reset */
 };
 
 /*
@@ -4561,8 +4565,10 @@ static int swevent_hlist_get(struct perf_event *event)
 static const struct pmu perf_ops_tracepoint = {
        .enable         = perf_trace_enable,
        .disable        = perf_trace_disable,
+       .start          = perf_swevent_int,
+       .stop           = perf_swevent_void,
        .read           = perf_swevent_read,
-       .unthrottle     = perf_swevent_unthrottle,
+       .unthrottle     = perf_swevent_void,
 };
 
 static int perf_tp_filter_match(struct perf_event *event,