From 3beaf903a3a07dc5c6500691b0b465d36292e3f8 Mon Sep 17 00:00:00 2001 From: Dani Liberman Date: Wed, 17 Nov 2021 09:59:10 +0200 Subject: [PATCH] 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 Reviewed-by: Oded Gabbay Signed-off-by: Oded Gabbay --- drivers/misc/habanalabs/common/command_submission.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/misc/habanalabs/common/command_submission.c b/drivers/misc/habanalabs/common/command_submission.c index c1fd4ba14c60e..4e893364a3cc7 100644 --- a/drivers/misc/habanalabs/common/command_submission.c +++ b/drivers/misc/habanalabs/common/command_submission.c @@ -545,6 +545,13 @@ static void complete_multi_cs(struct hl_device *hdev, struct hl_cs *cs) * mcs fences. */ fence->mcs_handling_done = true; + /* + * Since CS (and its related fence) can be associated with only one + * multi CS context, once it triggered multi CS completion no need to + * continue checking other multi CS contexts. + */ + spin_unlock(&mcs_compl->lock); + break; } spin_unlock(&mcs_compl->lock); -- 2.30.2