[PATCH v2 1/2][RFC] amdgpu: fix a race in kfd_mem_export_dmabuf()
Al Viro
viro at zeniv.linux.org.uk
Tue Jun 4 19:17:34 UTC 2024
[now without a descriptor leak; it really needs testing, though]
Using drm_gem_prime_handle_to_fd() to set dmabuf up and insert it into
descriptor table, only to have it looked up by file descriptor and
remove it from descriptor table is not just too convoluted - it's
racy; another thread might have modified the descriptor table while
we'd been going through that song and dance.
It's not hard to fix - turn drm_gem_prime_handle_to_fd()
into a wrapper for a new helper that would simply return the
dmabuf, without messing with descriptor table.
Then kfd_mem_export_dmabuf() would simply use that new helper
and leave the descriptor table alone.
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
---
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
index 8975cf41a91a..793780bb819c 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
@@ -25,7 +25,6 @@
#include <linux/pagemap.h>
#include <linux/sched/mm.h>
#include <linux/sched/task.h>
-#include <linux/fdtable.h>
#include <drm/ttm/ttm_tt.h>
#include <drm/drm_exec.h>
@@ -812,18 +811,13 @@ static int kfd_mem_export_dmabuf(struct kgd_mem *mem)
if (!mem->dmabuf) {
struct amdgpu_device *bo_adev;
struct dma_buf *dmabuf;
- int r, fd;
bo_adev = amdgpu_ttm_adev(mem->bo->tbo.bdev);
- r = drm_gem_prime_handle_to_fd(&bo_adev->ddev, bo_adev->kfd.client.file,
+ dmabuf = drm_gem_prime_handle_to_dmabuf(&bo_adev->ddev, bo_adev->kfd.client.file,
mem->gem_handle,
mem->alloc_flags & KFD_IOC_ALLOC_MEM_FLAGS_WRITABLE ?
- DRM_RDWR : 0, &fd);
- if (r)
- return r;
- dmabuf = dma_buf_get(fd);
- close_fd(fd);
- if (WARN_ON_ONCE(IS_ERR(dmabuf)))
+ DRM_RDWR : 0);
+ if (IS_ERR(dmabuf))
return PTR_ERR(dmabuf);
mem->dmabuf = dmabuf;
}
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 03bd3c7bd0dc..467c7a278ad3 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -409,23 +409,9 @@ static struct dma_buf *export_and_register_object(struct drm_device *dev,
return dmabuf;
}
-/**
- * drm_gem_prime_handle_to_fd - PRIME export function for GEM drivers
- * @dev: dev to export the buffer from
- * @file_priv: drm file-private structure
- * @handle: buffer handle to export
- * @flags: flags like DRM_CLOEXEC
- * @prime_fd: pointer to storage for the fd id of the create dma-buf
- *
- * This is the PRIME export function which must be used mandatorily by GEM
- * drivers to ensure correct lifetime management of the underlying GEM object.
- * The actual exporting from GEM object to a dma-buf is done through the
- * &drm_gem_object_funcs.export callback.
- */
-int drm_gem_prime_handle_to_fd(struct drm_device *dev,
+struct dma_buf *drm_gem_prime_handle_to_dmabuf(struct drm_device *dev,
struct drm_file *file_priv, uint32_t handle,
- uint32_t flags,
- int *prime_fd)
+ uint32_t flags)
{
struct drm_gem_object *obj;
int ret = 0;
@@ -434,14 +420,14 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
mutex_lock(&file_priv->prime.lock);
obj = drm_gem_object_lookup(file_priv, handle);
if (!obj) {
- ret = -ENOENT;
+ dmabuf = ERR_PTR(-ENOENT);
goto out_unlock;
}
dmabuf = drm_prime_lookup_buf_by_handle(&file_priv->prime, handle);
if (dmabuf) {
get_dma_buf(dmabuf);
- goto out_have_handle;
+ goto out;
}
mutex_lock(&dev->object_name_lock);
@@ -463,7 +449,6 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
/* normally the created dma-buf takes ownership of the ref,
* but if that fails then drop the ref
*/
- ret = PTR_ERR(dmabuf);
mutex_unlock(&dev->object_name_lock);
goto out;
}
@@ -478,34 +463,51 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
ret = drm_prime_add_buf_handle(&file_priv->prime,
dmabuf, handle);
mutex_unlock(&dev->object_name_lock);
- if (ret)
- goto fail_put_dmabuf;
-
-out_have_handle:
- ret = dma_buf_fd(dmabuf, flags);
- /*
- * We must _not_ remove the buffer from the handle cache since the newly
- * created dma buf is already linked in the global obj->dma_buf pointer,
- * and that is invariant as long as a userspace gem handle exists.
- * Closing the handle will clean out the cache anyway, so we don't leak.
- */
- if (ret < 0) {
- goto fail_put_dmabuf;
- } else {
- *prime_fd = ret;
- ret = 0;
+ if (ret) {
+ dma_buf_put(dmabuf);
+ dmabuf = ERR_PTR(ret);
}
-
- goto out;
-
-fail_put_dmabuf:
- dma_buf_put(dmabuf);
out:
drm_gem_object_put(obj);
out_unlock:
mutex_unlock(&file_priv->prime.lock);
+ return dmabuf;
+}
+EXPORT_SYMBOL(drm_gem_prime_handle_to_dmabuf);
- return ret;
+/**
+ * drm_gem_prime_handle_to_fd - PRIME export function for GEM drivers
+ * @dev: dev to export the buffer from
+ * @file_priv: drm file-private structure
+ * @handle: buffer handle to export
+ * @flags: flags like DRM_CLOEXEC
+ * @prime_fd: pointer to storage for the fd id of the create dma-buf
+ *
+ * This is the PRIME export function which must be used mandatorily by GEM
+ * drivers to ensure correct lifetime management of the underlying GEM object.
+ * The actual exporting from GEM object to a dma-buf is done through the
+ * &drm_gem_object_funcs.export callback.
+ */
+int drm_gem_prime_handle_to_fd(struct drm_device *dev,
+ struct drm_file *file_priv, uint32_t handle,
+ uint32_t flags,
+ int *prime_fd)
+{
+ struct dma_buf *dmabuf;
+ int fd = get_unused_fd_flags(flags);
+
+ if (fd < 0)
+ return fd;
+
+ dmabuf = drm_gem_prime_handle_to_dmabuf(dev, file_priv, handle, flags);
+ if (IS_ERR(dmabuf)) {
+ put_unused_fd(fd);
+ return PTR_ERR(dmabuf);
+ }
+
+ fd_install(fd, dmabuf->file);
+ *prime_fd = fd;
+ return 0;
}
EXPORT_SYMBOL(drm_gem_prime_handle_to_fd);
diff --git a/include/drm/drm_prime.h b/include/drm/drm_prime.h
index 2a1d01e5b56b..fa085c44d4ca 100644
--- a/include/drm/drm_prime.h
+++ b/include/drm/drm_prime.h
@@ -69,6 +69,9 @@ void drm_gem_dmabuf_release(struct dma_buf *dma_buf);
int drm_gem_prime_fd_to_handle(struct drm_device *dev,
struct drm_file *file_priv, int prime_fd, uint32_t *handle);
+struct dma_buf *drm_gem_prime_handle_to_dmabuf(struct drm_device *dev,
+ struct drm_file *file_priv, uint32_t handle,
+ uint32_t flags);
int drm_gem_prime_handle_to_fd(struct drm_device *dev,
struct drm_file *file_priv, uint32_t handle, uint32_t flags,
int *prime_fd);
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