[PATCH AUTOSEL for 4.9 195/293] powerpc/perf/hv-24x7: Fix off-by-one error in request_buffer check

[Sasha Levin]

From: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxxxxxxx>

[ Upstream commit 36c8fb2c616d9373758b155d9723774353067a87 ]

request_buffer can hold 254 requests, so if it already has that number of
entries we can't add a new one.

Also, define constant to show where the number comes from.

Fixes: e3ee15dc5d19 ("powerpc/perf/hv-24x7: Define add_event_to_24x7_request()")
Reviewed-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 arch/powerpc/perf/hv-24x7.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/perf/hv-24x7.c b/arch/powerpc/perf/hv-24x7.c
index 13cea4e8c56d..9fc2be138e32 100644
--- a/arch/powerpc/perf/hv-24x7.c
+++ b/arch/powerpc/perf/hv-24x7.c
@@ -166,6 +166,10 @@ DEFINE_PER_CPU(struct hv_24x7_hw, hv_24x7_hw);
 DEFINE_PER_CPU(char, hv_24x7_reqb[H24x7_DATA_BUFFER_SIZE]) __aligned(4096);
 DEFINE_PER_CPU(char, hv_24x7_resb[H24x7_DATA_BUFFER_SIZE]) __aligned(4096);
 
+#define MAX_NUM_REQUESTS	((H24x7_DATA_BUFFER_SIZE -		       \
+					sizeof(struct hv_24x7_request_buffer)) \
+					/ sizeof(struct hv_24x7_request))
+
 static char *event_name(struct hv_24x7_event_data *ev, int *len)
 {
 	*len = be16_to_cpu(ev->event_name_len) - 2;
@@ -1107,7 +1111,7 @@ static int add_event_to_24x7_request(struct perf_event *event,
 	int i;
 	struct hv_24x7_request *req;
 
-	if (request_buffer->num_requests > 254) {
+	if (request_buffer->num_requests >= MAX_NUM_REQUESTS) {
 		pr_devel("Too many requests for 24x7 HCALL %d\n",
 				request_buffer->num_requests);
 		return -EINVAL;
-- 
2.15.1