drm: Restore the NULL check for drm_gem_object_put()

Some users want to pass NULL to drm_gem_object_put(), but those using __drm_gem_object_put() did not. Compromise, have both and let the compiler sort it out. drm_gem_fb_destroy() calls drm_gem_object_put() with NULL obj causing: [ 11.584209] BUG: kernel NULL pointer dereference, address: 0000000000000000 [ 11.584213] #PF: supervisor write access in kernel mode [ 11.584215] #PF: error_code(0x0002) - not-present page [ 11.584216] PGD 0 P4D 0 [ 11.584220] Oops: 0002 [#1] SMP NOPTI [ 11.584223] CPU: 7 PID: 1571 Comm: gnome-shell Tainted: G E 5.7.0-rc1-1-default+ #27 [ 11.584225] Hardware name: Micro-Star International Co., Ltd. MS-7A31/X370 XPOWER GAMING TITANIUM (MS-7A31), BIOS 1.MR 12/03/2019 [ 11.584237] RIP: 0010:drm_gem_fb_destroy+0x28/0x70 [drm_kms_helper] <snip> [ 11.584256] Call Trace: [ 11.584279] drm_mode_rmfb+0x189/0x1c0 [drm] [ 11.584299] ? drm_mode_rmfb+0x1c0/0x1c0 [drm] [ 11.584314] drm_ioctl_kernel+0xaa/0xf0 [drm] [ 11.584329] drm_ioctl+0x1ff/0x3b0 [drm] [ 11.584347] ? drm_mode_rmfb+0x1c0/0x1c0 [drm] [ 11.584421] amdgpu_drm_ioctl+0x49/0x80 [amdgpu] [ 11.584427] ksys_ioctl+0x87/0xc0 [ 11.584430] __x64_sys_ioctl+0x16/0x20 [ 11.584434] do_syscall_64+0x5f/0x240 [ 11.584438] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 11.584440] RIP: 0033:0x7f0ef80f7227 Reported-by: Nirmoy Das <nirmoy.das@amd.com> Fixes: b5d2507 ("drm/gem: fold drm_gem_object_put_unlocked and __drm_gem_object_put()") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Nirmoy Das <nirmoy.das@amd.com> Cc: Emil Velikov <emil.velikov@collabora.com> Cc: Christian König <christian.koenig@amd.com>. Acked-by: Nirmoy Das <nirmoy.das@amd.com> Reviewed-by: Emil Velikov <emil.velikov@collabora.com> Link: https://patchwork.freedesktop.org/patch/msgid/20200520142347.29060-1-chris@chris-wilson.co.uk
intel · May 20, 2020 · 0e799e8 · 0e799e8
1 parent ef82555
commit 0e799e8
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Showing 2 changed files with 10 additions and 2 deletions.
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
@@ -105,7 +105,7 @@ __attribute__((nonnull))
 static inline void
 i915_gem_object_put(struct drm_i915_gem_object *obj)
 {
-	drm_gem_object_put(&obj->base);
+	__drm_gem_object_put(&obj->base);
 }
 
 #define assert_object_held(obj) dma_resv_assert_held((obj)->base.resv)

diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
@@ -363,6 +363,13 @@ static inline void drm_gem_object_get(struct drm_gem_object *obj)
 	kref_get(&obj->refcount);
 }
 
+__attribute__((nonnull))
+static inline void
+__drm_gem_object_put(struct drm_gem_object *obj)
+{
+	kref_put(&obj->refcount, drm_gem_object_free);
+}
+
 /**
  * drm_gem_object_put - drop a GEM buffer object reference
  * @obj: GEM buffer object
@@ -372,7 +379,8 @@ static inline void drm_gem_object_get(struct drm_gem_object *obj)
 static inline void
 drm_gem_object_put(struct drm_gem_object *obj)
 {
-	kref_put(&obj->refcount, drm_gem_object_free);
+	if (obj)
+		__drm_gem_object_put(obj);
 }
 
 void drm_gem_object_put_locked(struct drm_gem_object *obj);