Messages in this thread | | | Subject | Re: [PATCH] drm/prime: fix a potential double put (release) bug | From | Christian König <> | Date | Wed, 18 Aug 2021 15:25:59 +0200 |
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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@163.com> > --- > 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); > }
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