On 1/23/20 11:21 PM, Chris Wilson wrote:
The file is not part of the global drm resource and can be released
prior to take the global mutex to drop the open_count (and potentially
close) the drm device. As the global mutex is indeed global, not only
within the device but across devices, a slow file release mechanism can
bottleneck the entire system.
However, inside drm_close_helper() there are a number of dev->driver
callbacks that take the drm_device as the first parameter... Worryingly
some of those callbacks may be (implicitly) depending on the global
mutex.
From a quick audit, via, sis and vmwgfx are safe, so for those
Acked-by: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
Savage appears to be unsafe, due to unprotected access in the dma device
member. Haven't audited i810 or potential other drivers affected.
Perhaps it makes sense to enable lockfree filp release on a per-driver
basis to begin with?
/Thomas
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