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i#7044 sched deadlock: Fix theoretical deadlock #7087

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merged 4 commits into from
Nov 19, 2024
Merged

i#7044 sched deadlock: Fix theoretical deadlock #7087

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47bf896
i#7044 sched deadlock: Fix theoretical deadlock
derekbruening Nov 15, 2024
afb355a
Solve a 2nd theoretical lock issue: disallow holding the lock if we m…
derekbruening Nov 15, 2024
ea9b164
Add comment on avoiding hang if lock already held
derekbruening Nov 19, 2024
c65e5cc
Review request: update comment
derekbruening Nov 19, 2024
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9 changes: 8 additions & 1 deletion clients/drcachesim/scheduler/scheduler_impl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2292,6 +2292,8 @@ scheduler_impl_tmpl_t<RecordType, ReaderType>::set_cur_input(
// straightforward).
if (options_.mapping == sched_type_t::MAP_TO_ANY_OUTPUT && prev_input != input &&
!inputs_[prev_input].at_eof) {
// The caller should never hold the input lock for MAP_TO_ANY_OUTPUT.
assert(!caller_holds_cur_input_lock);
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add_to_ready_queue(output, &inputs_[prev_input]);
}
} else if (options_.schedule_record_ostream != nullptr &&
Expand All @@ -2313,7 +2315,12 @@ scheduler_impl_tmpl_t<RecordType, ReaderType>::set_cur_input(

int prev_workload = -1;
if (outputs_[output].prev_input >= 0 && outputs_[output].prev_input != input) {
std::lock_guard<mutex_dbg_owned> lock(*inputs_[outputs_[output].prev_input].lock);
// If the caller already holds the lock, do not re-acquire as that will hang.
auto scoped_lock =
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(caller_holds_cur_input_lock && prev_input == outputs_[output].prev_input)
? std::unique_lock<mutex_dbg_owned>()
: std::unique_lock<mutex_dbg_owned>(
*inputs_[outputs_[output].prev_input].lock);
prev_workload = inputs_[outputs_[output].prev_input].workload;
}

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3 changes: 2 additions & 1 deletion clients/drcachesim/scheduler/scheduler_impl.h
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Expand Up @@ -751,7 +751,8 @@ template <typename RecordType, typename ReaderType> class scheduler_impl_tmpl_t

// The caller cannot hold the output or input lock.
// The caller can hold the output's current input's lock but must pass
// true for the 3rd parameter in that case.
// true for the 3rd parameter in that case; holding the lock is not
// allowed for MAP_TO_ANY_OUTPUT.
stream_status_t
set_cur_input(output_ordinal_t output, input_ordinal_t input,
bool caller_holds_cur_input_lock = false);
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