Rewrite reap_dead_tasks to never grab the sched lock before a task lock
Doing so contradicts the locking order used everywhere else and causes deadlocks. Un-XFAIL task-perf-spawnalot Closes #854
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3 changed files with 47 additions and 9 deletions
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@ -100,25 +100,66 @@ rust_scheduler::number_of_live_tasks() {
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void
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rust_scheduler::reap_dead_tasks(int id) {
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I(this, lock.lock_held_by_current_thread());
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for (size_t i = 0; i < dead_tasks.length(); ) {
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if (dead_tasks.length() == 0) {
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return;
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}
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// First make up copy of the dead_task list with the lock held
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size_t dead_tasks_len = dead_tasks.length();
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rust_task **dead_tasks_copy = (rust_task**)
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srv->malloc(sizeof(rust_task*) * dead_tasks_len);
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for (size_t i = 0; i < dead_tasks_len; ++i) {
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rust_task *task = dead_tasks[i];
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dead_tasks_copy[i] = task;
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}
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// Now drop the lock and futz with the tasks. This avoids establishing
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// a sched->lock then task->lock locking order, which would be devestating
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// to performance.
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lock.unlock();
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for (size_t i = 0; i < dead_tasks_len; ++i) {
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rust_task *task = dead_tasks_copy[i];
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task->lock.lock();
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// Make sure this task isn't still running somewhere else...
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if (task->can_schedule(id)) {
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I(this, task->tasks_waiting_to_join.is_empty());
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dead_tasks.remove(task);
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DLOG(this, task,
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"deleting unreferenced dead task %s @0x%" PRIxPTR,
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task->name, task);
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task->lock.unlock();
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} else {
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task->lock.unlock();
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dead_tasks_copy[i] = NULL;
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}
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}
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// Now grab the lock again and remove the tasks that were truly dead
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lock.lock();
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for (size_t i = 0; i < dead_tasks_len; ++i) {
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rust_task *task = dead_tasks_copy[i];
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if (task) {
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dead_tasks.remove(task);
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}
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}
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// Now unlock again because we have to actually free the dead tasks,
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// and that may end up wanting to do lock the task and sched locks
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// again (via target->send)
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lock.unlock();
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for (size_t i = 0; i < dead_tasks_len; ++i) {
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rust_task *task = dead_tasks_copy[i];
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if (task) {
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task->deref();
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sync::decrement(kernel->live_tasks);
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kernel->wakeup_schedulers();
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continue;
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}
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task->lock.unlock();
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++i;
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}
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srv->free(dead_tasks_copy);
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lock.lock();
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}
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/**
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@ -90,6 +90,7 @@ rust_task::rust_task(rust_scheduler *sched, rust_task_list *state,
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rust_task::~rust_task()
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{
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I(sched, !sched->lock.lock_held_by_current_thread());
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DLOG(sched, task, "~rust_task %s @0x%" PRIxPTR ", refcnt=%d",
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name, (uintptr_t)this, ref_count);
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@ -1,7 +1,3 @@
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// xfail-stage1
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// xfail-stage2
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// xfail-stage3
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use std;
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import std::vec;
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import std::task;
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