fs/proc: do_task_stat: use sig->stats_lock to gather the threads/children stats

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kernel: fs/proc: do_task_stat: use sig->stats_lock to gather the threads/children stats

A vulnerability was found in the dotaskstat function in the Linux kernel, where due to excessive lock contention, a potential hard lockup could be created. This can create a performance bottleneck and lead to kernel unresponsiveness...