[PATCH AUTOSEL 6.18] drm/vc4: Protect madv read in vc4_gem_object_mmap() with madv_lock

[Sasha Levin]

From: Maíra Canal <mcanal@xxxxxxxxxx>

[ Upstream commit 338c56050d8e892604da97f67bfa8cc4015a955f ]

The mmap callback reads bo->madv without holding madv_lock, racing with
concurrent DRM_IOCTL_VC4_GEM_MADVISE calls that modify the field under
the same lock. Add the missing locking to prevent the data race.

Fixes: b9f19259b84d ("drm/vc4: Add the DRM_IOCTL_VC4_GEM_MADVISE ioctl")
Reviewed-by: Melissa Wen <mwen@xxxxxxxxxx>
Link: https://patch.msgid.link/20260330-vc4-misc-fixes-v1-4-92defc940a29@xxxxxxxxxx
Signed-off-by: Maíra Canal <mcanal@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---

LLM Generated explanations, may be completely bogus:

Error: Failed to generate final synthesis

 drivers/gpu/drm/vc4/vc4_bo.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_bo.c b/drivers/gpu/drm/vc4/vc4_bo.c
index 4aaa587be3a5e..a1efda9c39f92 100644
--- a/drivers/gpu/drm/vc4/vc4_bo.c
+++ b/drivers/gpu/drm/vc4/vc4_bo.c
@@ -738,12 +738,15 @@ static int vc4_gem_object_mmap(struct drm_gem_object *obj, struct vm_area_struct
 		return -EINVAL;
 	}
 
+	mutex_lock(&bo->madv_lock);
 	if (bo->madv != VC4_MADV_WILLNEED) {
 		DRM_DEBUG("mmapping of %s BO not allowed\n",
 			  bo->madv == VC4_MADV_DONTNEED ?
 			  "purgeable" : "purged");
+		mutex_unlock(&bo->madv_lock);
 		return -EINVAL;
 	}
+	mutex_unlock(&bo->madv_lock);
 
 	return drm_gem_dma_mmap(&bo->base, vma);
 }
-- 
2.53.0