On Fri, Jul 23, 2021 at 02:34:13PM +0200, Christian König wrote:
Am 23.07.21 um 14:31 schrieb Charan Teja Reddy:
It is expected from the clients to follow the below steps on an imported dmabuf fd: a) dmabuf = dma_buf_get(fd) // Get the dmabuf from fd b) dma_buf_attach(dmabuf); // Clients attach to the dmabuf o Here the kernel does some slab allocations, say for dma_buf_attachment and may be some other slab allocation in the dmabuf->ops->attach(). c) Client may need to do dma_buf_map_attachment(). d) Accordingly dma_buf_unmap_attachment() should be called. e) dma_buf_detach () // Clients detach to the dmabuf. o Here the slab allocations made in b) are freed. f) dma_buf_put(dmabuf) // Can free the dmabuf if it is the last reference.
Now say an erroneous client failed at step c) above thus it directly called dma_buf_put(), step f) above. Considering that it may be the last reference to the dmabuf, buffer will be freed with pending attachments left to the dmabuf which can show up as the 'memory leak'. This should at least be reported as the WARN().
Signed-off-by: Charan Teja Reddy charante@codeaurora.org
Good idea. I would expect a crash immediately, but from such a backtrace it is quite hard to tell what the problem is.
Patch is Reviewed-by: Christian König christian.koenig@amd.com and I'm going to push this to drm-misc-next on Monday if nobody objects.
The boom only happens a lot later when the offending import uses the attachment again. This here has a good chance to catch that early drm_buf_put(), so I think it's a good improvement. We'll still Oops later on ofc, but meh.
Acked-by: Daniel Vetter daniel.vetter@ffwll.ch
Thanks, Christian.
drivers/dma-buf/dma-buf.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 511fe0d..733c8b1 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -79,6 +79,7 @@ static void dma_buf_release(struct dentry *dentry) if (dmabuf->resv == (struct dma_resv *)&dmabuf[1]) dma_resv_fini(dmabuf->resv);
- WARN_ON(!list_empty(&dmabuf->attachments)); module_put(dmabuf->owner); kfree(dmabuf->name); kfree(dmabuf);