linux-kernel - [RFC 02/24] drm/gpuvm: Don't require obj lock in destructor path

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Message-ID: <20241207161651.410556-3-robdclark@gmail.com>
Date: Sat,  7 Dec 2024 08:15:02 -0800
From: Rob Clark <robdclark@...il.com>
To: dri-devel@...ts.freedesktop.org
Cc: freedreno@...ts.freedesktop.org,
	linux-arm-msm@...r.kernel.org,
	Connor Abbott <cwabbott0@...il.com>,
	Akhil P Oommen <quic_akhilpo@...cinc.com>,
	Rob Clark <robdclark@...omium.org>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	linux-kernel@...r.kernel.org (open list)
Subject: [RFC 02/24] drm/gpuvm: Don't require obj lock in destructor path

From: Rob Clark <robdclark@...omium.org>

See commit a414fe3a2129 ("drm/msm/gem: Drop obj lock in
msm_gem_free_object()") for justification.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/gpu/drm/drm_gpuvm.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
index f9eb56f24bef..1e89a98caad4 100644
--- a/drivers/gpu/drm/drm_gpuvm.c
+++ b/drivers/gpu/drm/drm_gpuvm.c
@@ -1511,7 +1511,9 @@ drm_gpuvm_bo_destroy(struct kref *kref)
 	drm_gpuvm_bo_list_del(vm_bo, extobj, lock);
 	drm_gpuvm_bo_list_del(vm_bo, evict, lock);
 
-	drm_gem_gpuva_assert_lock_held(obj);
+	if (kref_read(&obj->refcount) > 0)
+		drm_gem_gpuva_assert_lock_held(obj);
+
 	list_del(&vm_bo->list.entry.gem);
 
 	if (ops && ops->vm_bo_free)
@@ -1871,7 +1873,8 @@ drm_gpuva_unlink(struct drm_gpuva *va)
 	if (unlikely(!obj))
 		return;
 
-	drm_gem_gpuva_assert_lock_held(obj);
+	if (kref_read(&obj->refcount) > 0)
+		drm_gem_gpuva_assert_lock_held(obj);
 	list_del_init(&va->gem.entry);
 
 	va->vm_bo = NULL;
-- 
2.47.1