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Date: Thu, 20 Jul 2023 13:30:43 -0400
From: Rich Felker <dalias@...c.org>
To: Alexey Izbyshev <izbyshev@...ras.ru>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH] set tid address in fork
On Thu, Jul 20, 2023 at 05:22:07PM +0300, Alexey Izbyshev wrote:
> 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.
Yes, and the fix is in an unpushed commit. Sorry! I'll review queue
and push in a bit.
Rich
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