[tip:perf/urgent] perf: Fix crash in swevents

tip-bot for Peter Zijlstra
2010-06-03T17:55:28Z

Commit-ID: c6df8d5ab87a246942d138321e1721edbb69f6e1
Gitweb: http://git.kernel.org/tip/c6df8d5ab87a246942d138321e1721edbb69f6e1
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Thu, 3 Jun 2010 11:21:20 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 3 Jun 2010 17:03:08 +0200

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>
---
kernel/perf_event.c | 24 +++++++++++++++---------
1 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 858f56f..31d6afe 100644
--- 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,