drm/amd/amdgpu: fix missing lock for cper.ring->rptr/wptr access

commit 8e0d1ed upstream.

Add lock protection for 'ring->wptr'/'ring->rptr' to ensure the correct execution.

Fixes: 8652920 ("drm/amdgpu: add mutex lock for cper ring")
Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Yang Wang

drivers/gpu/drm/amd/amdgpu/amdgpu_cper.c

@@ -459,7 +459,7 @@ static u32 amdgpu_cper_ring_get_ent_sz(struct amdgpu_ring *ring, u64 pos)
 
 void amdgpu_cper_ring_write(struct amdgpu_ring *ring, void *src, int count)
 {
-	u64 pos, wptr_old, rptr = *ring->rptr_cpu_addr & ring->ptr_mask;
+	u64 pos, wptr_old, rptr;
 	int rec_cnt_dw = count >> 2;
 	u32 chunk, ent_sz;
 	u8 *s = (u8 *)src;
@@ -472,9 +472,11 @@ void amdgpu_cper_ring_write(struct amdgpu_ring *ring, void *src, int count)
 		return;
 	}
 
+	mutex_lock(&ring->adev->cper.ring_lock);
+
 	wptr_old = ring->wptr;
+	rptr = *ring->rptr_cpu_addr & ring->ptr_mask;
 
-	mutex_lock(&ring->adev->cper.ring_lock);
 	while (count) {
 		ent_sz = amdgpu_cper_ring_get_ent_sz(ring, ring->wptr);
 		chunk = umin(ent_sz, count);