Hi, it seems we can release spinlock twice in /src/backend/storage/ipc/procsignal.c file, method ProcSignalInit.
void
ProcSignalInit(bool cancel_key_valid, int32 cancel_key)
{
ProcSignalSlot *slot;
uint64 barrier_generation;
..............................................................................
slot = &ProcSignal->psh_slot[MyProcNumber];
/* sanity check */
SpinLockAcquire(&slot->pss_mutex);
if (pg_atomic_read_u32(&slot->pss_pid) != 0)
{
SpinLockRelease(&slot->pss_mutex);
elog(LOG, "process %d taking over ProcSignal slot %d, but it's not empty",
MyProcPid, MyProcNumber);
}
/* Clear out any leftover signal reasons */
MemSet(slot->pss_signalFlags, 0, NUM_PROCSIGNALS * sizeof(sig_atomic_t));
......................
slot->pss_cancel_key_valid = cancel_key_valid;
slot->pss_cancel_key = cancel_key;
pg_atomic_write_u32(&slot->pss_pid, MyProcPid);
SpinLockRelease(&slot->pss_mutex);
First in the if clause, second near the end of function. Such behavior can lead to unpredictable concurrent issues.
In applied patch I removed spinlock release in if clause.
