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fix queue locking behavior when creating event lists #1546

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Merged
kbenzie merged 1 commit into from
May 3, 2024
Merged

fix queue locking behavior when creating event lists #1546

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36 changes: 25 additions & 11 deletions source/adapters/level_zero/event.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1261,16 +1261,26 @@ ur_result_t _ur_ze_event_list_t::createAndRetainUrZeEventList(
}

auto Queue = EventList[I]->UrQueue;
if (Queue) {
// The caller of createAndRetainUrZeEventList must already hold
// a lock of the CurQueue. Additionally lock the Queue if it
// is different from CurQueue.
// TODO: rework this to avoid deadlock when another thread is
// locking the same queues but in a different order.
auto Lock = ((Queue == CurQueue)
? std::unique_lock<ur_shared_mutex>()
: std::unique_lock<ur_shared_mutex>(Queue->Mutex));

auto CurQueueDevice = CurQueue->Device;
std::optional<std::unique_lock<ur_shared_mutex>> QueueLock =
std::nullopt;
// The caller of createAndRetainUrZeEventList must already hold
// a lock of the CurQueue. However, if the CurQueue is different
// then the Event's Queue, we need to drop that lock and
// acquire the Event's Queue lock. This is done to avoid a lock
// ordering issue.
// For the rest of this scope, CurQueue cannot be accessed.
// TODO: This solution is very error-prone. This requires a refactor
// to either have fine-granularity locks inside of the queues or
// to move any operations on queues other than CurQueue out
// of this scope.
if (Queue && Queue != CurQueue) {
CurQueue->Mutex.unlock();
QueueLock = std::unique_lock<ur_shared_mutex>(Queue->Mutex);
}

if (Queue) {
// If the event that is going to be waited is in an open batch
// different from where this next command is going to be added,
// then we have to force execute of that open command-list
Expand Down Expand Up @@ -1313,7 +1323,7 @@ ur_result_t _ur_ze_event_list_t::createAndRetainUrZeEventList(
}

ur_command_list_ptr_t CommandList;
if (Queue && Queue->Device != CurQueue->Device) {
if (Queue && Queue->Device != CurQueueDevice) {
// Get a command list prior to acquiring an event lock.
// This prevents a potential deadlock with recursive
// event locks.
Expand All @@ -1323,7 +1333,7 @@ ur_result_t _ur_ze_event_list_t::createAndRetainUrZeEventList(

std::shared_lock<ur_shared_mutex> Lock(EventList[I]->Mutex);

if (Queue && Queue->Device != CurQueue->Device &&
if (Queue && Queue->Device != CurQueueDevice &&
!EventList[I]->IsMultiDevice) {
ze_event_handle_t MultiDeviceZeEvent = nullptr;
ur_event_handle_t MultiDeviceEvent;
Expand Down Expand Up @@ -1357,6 +1367,10 @@ ur_result_t _ur_ze_event_list_t::createAndRetainUrZeEventList(
this->UrEventList[TmpListLength]->RefCount.increment();
}

if (QueueLock.has_value()) {
QueueLock.reset();
CurQueue->Mutex.lock();
}
TmpListLength += 1;
}
}
Expand Down