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6c1c116a0f
When a resource is un-referenced, the reference count is decremented,
and intentionally no lock is acquired. This can result in the following
race condition when a resource is created from a handle:
```
[Thread] Operation
[0] Create resource from handle for the first time, refcount set to 1
[0] resource is unreferenced, refcount is decremented to 0 (intentionally
no mutex is locked)
[0] before entering virgl_hw_res_destroy to lock
virgl_drm_winsys::bo_handles_mutex the thread yields
[1] Create resource from handle pulls the resource from
virgl_drm_winsys::bo_handles, refcount is incremented to 1
[1] resource is unreferenced, refcount is decremented to 0
[1] Enter virgl_hw_res_destroy,
[1] acquire the lock on virgl_drm_winsys::bo_handles_mutex
[1] check reference count to be 0, yes -> the resource is destroyed
[1] release the lock on virgl_drm_winsys::bo_handles_mutex
[0] Enter virgl_hw_res_destroy,
[0] acquire the lock on virgl_drm_winsys::bo_handles_mutex
[0] Here the res pointer already points to freed memory
[0] check reference count to be 0, yes -> the resource is destroyed (again!)
double free or corruption (!prev)
```
To work around this race condition, keep track of the number of times
the resource was pulled from virgl_drm_winsys::bo_handles to see whether
it has to be kept alive despite the reference count being zero.
This can be reproduced with the `spec@ext_image_dma_buf_import@ext_image_dma_buf_import-refcount-multithread`
piglit test.
Signed-off-by: Corentin Noël <corentin.noel@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34809>
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`Mesa <https://mesa3d.org>`_ - The 3D Graphics Library ====================================================== Source ------ This repository lives at https://gitlab.freedesktop.org/mesa/mesa. Other repositories are likely forks, and code found there is not supported. Build & install --------------- You can find more information in our documentation (`docs/install.rst <https://docs.mesa3d.org/install.html>`_), but the recommended way is to use Meson (`docs/meson.rst <https://docs.mesa3d.org/meson.html>`_): .. code-block:: sh $ meson setup build $ ninja -C build/ $ sudo ninja -C build/ install Support ------- Many Mesa devs hang on IRC; if you're not sure which channel is appropriate, you should ask your question on `OFTC's #dri-devel <irc://irc.oftc.net/dri-devel>`_, someone will redirect you if necessary. Remember that not everyone is in the same timezone as you, so it might take a while before someone qualified sees your question. To figure out who you're talking to, or which nick to ping for your question, check out `Who's Who on IRC <https://dri.freedesktop.org/wiki/WhosWho/>`_. The next best option is to ask your question in an email to the mailing lists: `mesa-dev\@lists.freedesktop.org <https://lists.freedesktop.org/mailman/listinfo/mesa-dev>`_ Bug reports ----------- If you think something isn't working properly, please file a bug report (`docs/bugs.rst <https://docs.mesa3d.org/bugs.html>`_). Contributing ------------ Contributions are welcome, and step-by-step instructions can be found in our documentation (`docs/submittingpatches.rst <https://docs.mesa3d.org/submittingpatches.html>`_). Note that Mesa uses gitlab for patches submission, review and discussions.