Re: [PATCH] drm/prime: fix a potential double put (release) bug

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Am 18.08.21 um 15:02 schrieb Wentao_Liang:
In line 317 (#1), drm_gem_prime_import() is called, it will call
drm_gem_prime_import_dev(). At the end of the function
drm_gem_prime_import_dev() (line 956, #2), "dma_buf_put(dma_buf);" puts
dma_buf->file and may cause it to be released. However, after
drm_gem_prime_import() returning, the dma_buf may be put again by the
same put function in lines 342, 351 and 358 (#3, #4, #5). Putting the
dma_buf improperly more than once can lead to an incorrect dma_buf-
file put.
We believe that the put of the dma_buf in the function
drm_gem_prime_import() is unnecessary (#2). We can fix the above bug by
removing the redundant "dma_buf_put(dma_buf);" in line 956.

Guys I'm getting tired of NAKing those incorrect reference count analysis.

The dma_buf_put() in the error handling of drm_gem_prime_import_dev() function is balanced with the get_dma_buf() in the same function directly above.

This is for the creating a GEM object for a DMA-buf imported from other device use case and certainly correct.

The various dma_buf_put() in drm_gem_prime_fd_to_handle() is balanced with the dma_buf_get(prime_fd) at the beginning of the function.

This is for extracting the DMA-buf from the file descriptor and keeping a reference to it while we are busy importing it (e.g. to prevent a race when somebody changes the fd at the same time).

As far as I can see this is correct as well.

Regards,
Christian.


  314     if (dev->driver->gem_prime_import)
  315         obj = dev->driver->gem_prime_import(dev, dma_buf);
  316     else
  317         obj = drm_gem_prime_import(dev, dma_buf);
  				//#1 call to drm_gem_prime_import
				//   ->drm_gem_prime_import_dev
				//   ->dma_buf_put
  ...

  336     ret = drm_prime_add_buf_handle(&file_priv->prime,
  337             dma_buf, *handle);

  ...

  342     dma_buf_put(dma_buf);  //#3 put again
  343
  344     return 0;
  345
  346 fail:

  351     dma_buf_put(dma_buf); //#4 put again
  352     return ret;

  356 out_put:
  357     mutex_unlock(&file_priv->prime.lock);
  358     dma_buf_put(dma_buf);  //#5 put again
  359     return ret;
  360 }

  905 struct drm_gem_object *drm_gem_prime_import_dev
  							(struct drm_device *dev,
  906                         struct dma_buf *dma_buf,
  907                         struct device *attach_dev)
  908 {

  ...

  952 fail_unmap:
  953     dma_buf_unmap_attachment(attach, sgt, DMA_BIDIRECTIONAL);
  954 fail_detach:
  955     dma_buf_detach(dma_buf, attach);
  956     dma_buf_put(dma_buf);  //#2 the first put of dma_buf
								//	 (unnecessary)
  957
  958     return ERR_PTR(ret);
  959 }

Signed-off-by: Wentao_Liang <Wentao_Liang_g@xxxxxxx>
---
  drivers/gpu/drm/drm_prime.c | 1 -
  1 file changed, 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 2a54f86856af..cef03ad0d5cd 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -953,7 +953,6 @@ struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
  	dma_buf_unmap_attachment(attach, sgt, DMA_BIDIRECTIONAL);
  fail_detach:
  	dma_buf_detach(dma_buf, attach);
-	dma_buf_put(dma_buf);
return ERR_PTR(ret);
  }




[Index of Archives]     [Linux Input]     [Video for Linux]     [Gstreamer Embedded]     [Mplayer Users]     [Linux USB Devel]     [Linux Audio Users]     [Linux Kernel]     [Linux SCSI]     [Yosemite Backpacking]

  Powered by Linux