drm/msm: use trylock for debugfs

[ 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>

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 2995e80fec3ba98b9d161e04ce11571454dd7622..ebd8a360335966592f2712aab19c8a554b83a7be 100644 (file)
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -963,7 +963,8 @@ 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 ba5c4ff76292cac70038a89618b96530e3bd8545..ea001b0a6b6466c13bc54d48a94a0097a56f6be9 100644 (file)
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -188,6 +188,12 @@ 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)
 {