[PATCH] drm/v3d: Fix null pointer dereference of pointer perfmon

[Colin Ian King]

In the unlikely event that pointer perfmon is null the WARN_ON return path
occurs after the pointer has already been deferenced. Fix this by only
dereferencing perfmon after it has been null checked.

Fixes: 26a4dc29b74a ("drm/v3d: Expose performance counters to userspace")
Signed-off-by: Colin Ian King <colin.i.k...@gmail.com>
---
 drivers/gpu/drm/v3d/v3d_perfmon.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/v3d/v3d_perfmon.c 
b/drivers/gpu/drm/v3d/v3d_perfmon.c
index 0288ef063513..f6a88abccc7d 100644
--- a/drivers/gpu/drm/v3d/v3d_perfmon.c
+++ b/drivers/gpu/drm/v3d/v3d_perfmon.c
@@ -25,11 +25,12 @@ void v3d_perfmon_start(struct v3d_dev *v3d, struct 
v3d_perfmon *perfmon)
 {
        unsigned int i;
        u32 mask;
-       u8 ncounters = perfmon->ncounters;
+       u8 ncounters;
 
        if (WARN_ON_ONCE(!perfmon || v3d->active_perfmon))
                return;
 
+       ncounters = perfmon->ncounters;
        mask = GENMASK(ncounters - 1, 0);
 
        for (i = 0; i < ncounters; i++) {
-- 
2.35.1