Fix some random crashes when using metal argument buffers #2340
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Fixes an issue with BitArray enumeration, where it could iterate over bit indices that weren't set This would cause issues in descriptor set allocation, when argument buffers are enabled, where it could select a set index from the pool that isn't freed, and try to create a new set on top of the exiting one
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cdavis5e
approved these changes
Sep 18, 2024
billhollings
approved these changes
Sep 18, 2024
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Holy moly! Good catch! Thanks for submitting this!
Hard to believe that I typed that broken code 3 years ago, and that it has not been caught earlier. This kind of mistake should have been failing fast, but nothing in the millions of CTS tests have triggered it.
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Commit should fix a bug with the loop iteration in
enumerateEnabledBits(). It would jump to the first set bit, then iterate over EVERY subsequent bit, instead of only iterating over bits that were setDiscovered this after a lot of time debugging random crashes in MoltenVK 1.2.11, that would only happen with
MVK_CONFIG_USE_METAL_ARGUMENT_BUFFERSenabledWhat seemed to be happening was:
MVKDescriptorPool::allocateDescriptorSet()would iterate over_descriptorSetAvailablilityto find an empty set, but it would check sets that weren't freed yet.If one of those got picked, the new set is initialized on top of an existing one, essentially corrupting it. Odd behavior would happen after that, and the app would eventually crash trying to use the corrupted set
These crashes could only happen when using Metal Argument buffers, and using a pool with
VK_DESCRIPTOR_POOL_CREATE_FREE_DESCRIPTOR_SET_BITThis is a pretty simple change, so hopefully it doesn't break anything 😃