[PATCH 3.16.y-ckt 16/17] drm/radeon: hold reference to fences in radeon_sa_bo_new (3.17 and older)

[Luis Henriques <luis.henriques@canonical.com>]

3.16.7-ckt27 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: =?UTF-8?q?Nicolai=20H=C3=A4hnle?= <nicolai.haehnle@amd.com>

commit f6ff4f67cdf8455d0a4226eeeaf5af17c37d05eb upstream.

An arbitrary amount of time can pass between spin_unlock and
radeon_fence_wait_any, so we need to ensure that nobody frees the
fences from under us.

Based on the analogous fix for amdgpu.

Signed-off-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com> (v1 + fix)
Tested-by: Lutz Euler <lutz.euler@freenet.de>
[ nicolai:
 Backport of upstream commit f6ff4f67cdf8455d0a4226eeeaf5af17c37d05eb, with
 an additional NULL pointer guard that is required for kernels 3.17 and older.

 To be precise, any kernel that does *not* have commit 954605ca3 "drm/radeon:
 use common fence implementation for fences, v4" requires this additional
 NULL pointer guard.]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 drivers/gpu/drm/radeon/radeon_sa.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/radeon/radeon_sa.c b/drivers/gpu/drm/radeon/radeon_sa.c
index adcf3e2f07da..ef86509fe5f6 100644
--- a/drivers/gpu/drm/radeon/radeon_sa.c
+++ b/drivers/gpu/drm/radeon/radeon_sa.c
@@ -349,8 +349,15 @@ int radeon_sa_bo_new(struct radeon_device *rdev,
 			/* see if we can skip over some allocations */
 		} while (radeon_sa_bo_next_hole(sa_manager, fences, tries));
 
+		for (i = 0; i < RADEON_NUM_RINGS; ++i) {
+			if (fences[i])
+				radeon_fence_ref(fences[i]);
+		}
+
 		spin_unlock(&sa_manager->wq.lock);
 		r = radeon_fence_wait_any(rdev, fences, false);
+		for (i = 0; i < RADEON_NUM_RINGS; ++i)
+			radeon_fence_unref(&fences[i]);
 		spin_lock(&sa_manager->wq.lock);
 		/* if we have nothing to wait for block */
 		if (r == -ENOENT) {