Date: Fri, 6 Feb 2004 10:06:16 +0800 (CST) From: =?gb2312?q?popsong=20old?= <oldpopsong@yahoo.com> To: John Baldwin <jhb@FreeBSD.org> Cc: freebsd-current@freebsd.org Subject: Re: three locks and lock order reversal? Message-ID: <20040206020616.12702.qmail@web60606.mail.yahoo.com> In-Reply-To: <200402051418.54247.jhb@FreeBSD.org>
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> If one thread does A then B, another thread does B then C, and a third thread > does C then A you can deadlock if each thread gets the first lock and blocks > on the second lock. Thread 1 wants B and holds A, thread 2 holds B and wants > C, and thread 3 wants A and holds C. Thread 3 will not giveup C until it > gets A. Thread 1 holds A and won't give it up until it gets B. Thread 2 > holds B and won't give it up until it gets C which is held by thread 3. > Hence, deadlock. > > -- > John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ > "Power Users Use the Power to Serve" = http://www.FreeBSD.org > Thank you for the explanation! I only thought of two threads. So this bring me another question: if the machine only have 2 CPUs, does it mean that this kind of LOR is safe, provided there is no other sleep lock between A and B, B and C, C and A? song _________________________________________________________ Do You Yahoo!? 完全免费的雅虎电邮，马上注册获赠额外60兆网络存储空间 http://cn.rd.yahoo.com/mail_cn/tag/?http://cn.mail.yahoo.com
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