perf/x86/intel/pt: Fix and clean up error handling in pt_event_add()

Dan Carpenter reported that pt_event_add() has buggy
error handling logic: it returns 0 instead of -EBUSY when
it fails to start a newly added event.

Furthermore, the control flow in this function is messy,
with cleanup labels mixed with direct returns.

Fix the bug and clean up the code by converting it to
a straight fast path for the regular non-failing case,
plus a clear sequence of cascading goto labels to do
all cleanup.

NOTE: I materially changed the existing clean up logic in the
pt_event_start() failure case to use the direct
perf_aux_output_end() path, not pt_event_del(), because
perf_aux_output_end() is enough here.

Reported-by: Dan Carpenter <[email protected]>
Acked-by: Alexander Shishkin <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Julia Lawall <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

1 files changed, 15 insertions, 18 deletions

diff --git a/arch/x86/kernel/cpu/perf_event_intel_pt.c b/arch/x86/kernel/cpu/perf_event_intel_pt.c
index f2770641c0fd..ffe666c2c6b5 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_pt.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_pt.c
@@ -988,39 +988,36 @@ static int pt_event_add(struct perf_event *event, int mode)
 	int ret = -EBUSY;
 
 	if (pt->handle.event)
-		goto out;
+		goto fail;
 
 	buf = perf_aux_output_begin(&pt->handle, event);
-	if (!buf) {
-		ret = -EINVAL;
-		goto out;
-	}
+	ret = -EINVAL;
+	if (!buf)
+		goto fail_stop;
 
 	pt_buffer_reset_offsets(buf, pt->handle.head);
 	if (!buf->snapshot) {
 		ret = pt_buffer_reset_markers(buf, &pt->handle);
-		if (ret) {
-			perf_aux_output_end(&pt->handle, 0, true);
-			goto out;
-		}
+		if (ret)
+			goto fail_end_stop;
 	}
 
 	if (mode & PERF_EF_START) {
 		pt_event_start(event, 0);
-		if (hwc->state == PERF_HES_STOPPED) {
-			pt_event_del(event, 0);
-			ret = -EBUSY;
-		}
+		ret = -EBUSY;
+		if (hwc->state == PERF_HES_STOPPED)
+			goto fail_end_stop;
 	} else {
 		hwc->state = PERF_HES_STOPPED;
 	}
 
-	ret = 0;
-out:
-
-	if (ret)
-		hwc->state = PERF_HES_STOPPED;
+	return 0;
 
+fail_end_stop:
+	perf_aux_output_end(&pt->handle, 0, true);
+fail_stop:
+	hwc->state = PERF_HES_STOPPED;
+fail:
 	return ret;
 }