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.king@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

On Sun, 2022-04-24 at 19:35 +0100, Colin Ian King wrote:
> 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.
> 

Good catch!

Reviewed-by: Juan A. Suarez <jasuarez@igalia.com>


	J.A.

On 04/25, Juan A. Suárez wrote:
> On Sun, 2022-04-24 at 19:35 +0100, Colin Ian King wrote:
> > 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.
> > 
> 
> Good catch!
> 
> Reviewed-by: Juan A. Suarez <jasuarez@igalia.com>

Applied to drm-misc-next.

Thanks,

Melissa
> 
> 
> 	J.A.
>