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habanalabs: fix race condition in multi CS completion
Race example scenario: 1. User have 2 threads that waits on multi CS: - thread_0 waits on QID 0 and uses multi CS context 0. - thread_1 waits on QID 1 and uses multi CS context 1. 2. thread_1 got completion and release multi CS context 1. 3. CS related to multi CS of thread_0 starts executing complete_multi_cs function, the first iteration of the loop completes the multi CS of thread_0, hence multi CS context 0 is released. 4. thread_1 waits on QID 1 and uses multi CS context 0. 5. thread_0 waits on QID 0 and uses multi CS context 1. 6. The second iterattion of the loop (from step 3) starts, which means, start checking multi CS context 1: - multi CS contetxt is being used by thread_0 waiting on QID 0. - The fence of the CS (still CS from step 3) has QID map the same as the multi CS context 1. - multi CS context 1 (thread_0) gets completion on CS that triggered already thread_0 (with multi CS context 0) and is no longer being waited on. Fixed by exiting the loop in complete_multi_cs after getting completion Signed-off-by: Dani Liberman <dliberman@habana.ai> Reviewed-by: Oded Gabbay <ogabbay@kernel.org> Signed-off-by: Oded Gabbay <ogabbay@kernel.org>
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@ -545,6 +545,13 @@ static void complete_multi_cs(struct hl_device *hdev, struct hl_cs *cs)
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* mcs fences.
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*/
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fence->mcs_handling_done = true;
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/*
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* Since CS (and its related fence) can be associated with only one
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* multi CS context, once it triggered multi CS completion no need to
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* continue checking other multi CS contexts.
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*/
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spin_unlock(&mcs_compl->lock);
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break;
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}
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spin_unlock(&mcs_compl->lock);
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