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Date: Thu, 20 Jul 2023 17:22:07 +0300
From: Alexey Izbyshev <izbyshev@ispras.ru>
To: musl@lists.openwall.com
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Subject: Re: [musl] [PATCH] set tid address in fork

On 2023-07-20 16:53, changdiankang wrote:
> In pthrad_exit the exiting thread will hold the thread list lock,
> and will unlock it in kernel by clear the tid address 
> &__thread_list_lock.
> 
> A thread created by pthrad_create is created with clone syscall with
> CLONE_CHILD_CLEARTID flag and &__thread_list_lock as child_tid
> parameter. When the thread exits, the thread list lock can be woke up
> (see man clone CLONE_CHILD_CLEARTID).
> 
> But in fork, the main thread is created with fork syscall or with
> clone syscall without CLONE_CHILD_CLEARTID flag. The 
> &__thread_list_lock
> is not be set to tid address. So when the main thread exits, the thread
> list lock can't be woke up by kernel. This may lead some problems when
> other child threads try to hold this lock. For example, a child thread
> blocks at waiting thread list lock when joining the main thread.
> 
> To fix this issue, we should set &__thread_list_lock to the main thread 
> tid
> address in fork.

This bug has already been discovered, see 
https://www.openwall.com/lists/musl/2023/06/01/9.

Alexey