[PATCH v2 2/6] drm/msm: fix framebuffer pin refcount leak on prepare failure

[Dmitry Baryshkov]

msm_framebuffer_prepare() bumps prepare_count before pinning, but returns
straight out of the pin loop on error, leaking the count, the
msm_gem_vma_get() reference and any planes already pinned.
drm_atomic_helper_prepare_planes() does not call cleanup_fb() for the
plane whose prepare_fb() failed, so nothing ever drops it.

Since commit 8ac37c88f991 ("drm/msm: Refcount framebuffer pins") a
prepare which finds the count already non-zero returns early, assuming
iova[] is populated.  With the count stuck, every later prepare of that
framebuffer reports success while iova[] is still zero, and DPU scans out
from a NULL base address:

  arm-smmu 15000000.iommu: Unhandled context fault: fsr=0x402,
      iova=0x00000100, fsynr=0x3e0023, cbfrsynra=0x1c00, cb=11

Unwind properly on failure instead.

Fixes: 8ac37c88f991 ("drm/msm: Refcount framebuffer pins")
Assisted-by: LLM
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/msm/msm_fb.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/msm_fb.c b/drivers/gpu/drm/msm/msm_fb.c
index d69591245231..dfe040d5260b 100644
--- a/drivers/gpu/drm/msm/msm_fb.c
+++ b/drivers/gpu/drm/msm/msm_fb.c
@@ -102,13 +102,28 @@ int msm_framebuffer_prepare(struct drm_framebuffer *fb, bool needs_dirtyfb)
 		ret = msm_gem_get_and_pin_iova(fb->obj[i], vm, &msm_fb->iova[i]);
 		drm_dbg_state(fb->dev, "FB[%u]: iova[%d]: %08llx (%d)\n",
 			      fb->base.id, i, msm_fb->iova[i], ret);
-		if (ret)
+		if (ret) {
+			msm_gem_vma_put(fb->obj[i]);
 			break;
+		}
+	}
+
+	if (ret) {
+		while (i--) {
+			msm_gem_unpin_iova(fb->obj[i], vm);
+			msm_gem_vma_put(fb->obj[i]);
+		}
+
+		memset(msm_fb->iova, 0, sizeof(msm_fb->iova));
+		msm_fb->prepare_count--;
 	}
 
 out:
 	mutex_unlock(&msm_fb->lock);
 
+	if (ret && needs_dirtyfb)
+		refcount_dec(&msm_fb->dirtyfb);
+
 	return ret;
 }
 

-- 
2.47.3