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Date: Thu, 5 May 2016 18:20:35 +0100
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From: Martin Simmons <martin@lispworks.com>
To: Konstantin Belousov <kostikbel@gmail.com>
CC: threads@freebsd.org, arch@freebsd.org
In-reply-to: <20160505131029.GE2422@kib.kiev.ua> (message from Konstantin
 Belousov on Thu, 5 May 2016 16:10:29 +0300)
Subject: Re: Robust mutexes implementation
References: <20160505131029.GE2422@kib.kiev.ua>
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There is a potential bug in enqueue_mutex when it tests m1 == NULL and m1 !=
NULL.  These tests only work because m_lock is the first slot in struct
pthread_mutex and hence 0 in curthread->robust_list is converted to NULL
(rather than a negative value).

Also, is it safe to assume memory ordering between the assignments of
m->m_lock.m_rb_lnk and curthread->robust_list?  Maybe it is OK because the
kernel will never read curthread->robust_list until after the CPU executing
enqueue_mutex has passed a memory barrier?

__Martin