[sr-dev] [kamailio/kamailio] the recursive lock of tm module is not safe? (Issue #3083)

[progromm]

### Description
See `lock_hash` in `h_table.c`: 

```C
void lock_hash(int i)
{
    int mypid;

    mypid = my_pid();
    if (likely(atomic_get(&_tm_table->entries[i].locker_pid) != mypid)) {
        lock(&_tm_table->entries[i].mutex);
        atomic_set(&_tm_table->entries[i].locker_pid, mypid);
    } else {
        /* locked within the same process that called us*/
        _tm_table->entries[i].rec_lock_level++;
    }
}
```

Flowing lines of code do not guarantee atomicity and I think it is not safe:
* atomic_get(&_tm_table->entries[i].locker_pid) != mypid
* lock(&_tm_table->entries[i].mutex)
* atomic_set(&_tm_table->entries[i].locker_pid, mypid)

Would you mind solving my confusion?


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