[PATCH][next] perf/x86/intel/bts: check if bts_ctx is allocated when call bts functions

[lirongqing]

From: Li RongQing <lirongqing@xxxxxxxxx>

bts_ctx maybe not allocated, for example if the cpu has X86_FEATURE_PTI,
but intel_bts_disable/enable_local and intel_bts_interrupt are called
unconditionally from intel_pmu_handle_irq and exploding on accessing
bts_ctx

so check if bts_ctx is allocated when call bts functions

Fixes: 3acfcefa795c "(perf/x86/intel/bts: Allocate bts_ctx only if necessary)"
Reported-by: Jiri Olsa <olsajiri@xxxxxxxxx>
Suggested-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx>
Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
---
 arch/x86/events/intel/bts.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index 8e09319..e8b3e7b 100644
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -338,9 +338,14 @@ static void bts_event_stop(struct perf_event *event, int flags)
 
 void intel_bts_enable_local(void)
 {
-	struct bts_ctx *bts = this_cpu_ptr(bts_ctx);
-	int state = READ_ONCE(bts->state);
+	struct bts_ctx *bts;
+	int state;
 
+	if (!bts_ctx)
+		return;
+
+	bts = this_cpu_ptr(bts_ctx);
+	state = READ_ONCE(bts->state);
 	/*
 	 * Here we transition from INACTIVE to ACTIVE;
 	 * if we instead are STOPPED from the interrupt handler,
@@ -358,7 +363,12 @@ void intel_bts_enable_local(void)
 
 void intel_bts_disable_local(void)
 {
-	struct bts_ctx *bts = this_cpu_ptr(bts_ctx);
+	struct bts_ctx *bts;
+
+	if (!bts_ctx)
+		return;
+
+	bts = this_cpu_ptr(bts_ctx);
 
 	/*
 	 * Here we transition from ACTIVE to INACTIVE;
@@ -450,12 +460,17 @@ bts_buffer_reset(struct bts_buffer *buf, struct perf_output_handle *handle)
 int intel_bts_interrupt(void)
 {
 	struct debug_store *ds = this_cpu_ptr(&cpu_hw_events)->ds;
-	struct bts_ctx *bts = this_cpu_ptr(bts_ctx);
-	struct perf_event *event = bts->handle.event;
+	struct bts_ctx *bts;
+	struct perf_event *event;
 	struct bts_buffer *buf;
 	s64 old_head;
 	int err = -ENOSPC, handled = 0;
 
+	if (!bts_ctx)
+		return 0;
+
+	bts = this_cpu_ptr(bts_ctx);
+	event = bts->handle.event;
 	/*
 	 * The only surefire way of knowing if this NMI is ours is by checking
 	 * the write ptr against the PMI threshold.
-- 
2.9.4