releases/6.1.149/drm-msm-use-trylock-for-debugfs.patch

From df317cc14fbbe58fc26d444c33347e195a4b32bb Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Sun, 29 Jun 2025 13:13:22 -0700
Subject: drm/msm: use trylock for debugfs

From: Rob Clark <robdclark@chromium.org>

[ Upstream commit 0a1ff88ec5b60b41ba830c5bf08b6cd8f45ab411 ]

This resolves a potential deadlock vs msm_gem_vm_close().  Otherwise for
_NO_SHARE buffers msm_gem_describe() could be trying to acquire the
shared vm resv, while already holding priv->obj_lock.  But _vm_close()
might drop the last reference to a GEM obj while already holding the vm
resv, and msm_gem_free_object() needs to grab priv->obj_lock, a locking
inversion.

OTOH this is only for debugfs and it isn't critical if we undercount by
skipping a locked obj.  So just use trylock() and move along if we can't
get the lock.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>
Tested-by: Antonino Maniscalco <antomani103@gmail.com>
Reviewed-by: Antonino Maniscalco <antomani103@gmail.com>
Patchwork: https://patchwork.freedesktop.org/patch/661525/
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/msm/msm_gem.c | 3 ++-
 drivers/gpu/drm/msm/msm_gem.h | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 1dee0d18abbb..7116c2aac4cb 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -874,7 +874,8 @@ void msm_gem_describe(struct drm_gem_object *obj, struct seq_file *m,
 	uint64_t off = drm_vma_node_start(&obj->vma_node);
 	const char *madv;
 
-	msm_gem_lock(obj);
+	if (!msm_gem_trylock(obj))
+		return;
 
 	stats->all.count++;
 	stats->all.size += obj->size;
diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
index c4844cf3a585..4c8e0a022c24 100644
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -185,6 +185,12 @@ msm_gem_lock(struct drm_gem_object *obj)
 	dma_resv_lock(obj->resv, NULL);
 }
 
+static inline bool __must_check
+msm_gem_trylock(struct drm_gem_object *obj)
+{
+	return dma_resv_trylock(obj->resv);
+}
+
 static inline int
 msm_gem_lock_interruptible(struct drm_gem_object *obj)
 {
-- 
2.39.5