Date: Fri, 01 Oct 2004 00:13:01 -0400 From: Stephan Uphoff <ups@tree.com> To: John Baldwin <jhb@FreeBSD.org> Cc: "freebsd-arch@freebsd.org" <freebsd-arch@FreeBSD.org> Subject: Re: scheduler (sched_4bsd) questions Message-ID: <1096603981.21577.195.camel@palm.tree.com> In-Reply-To: <1096496057.3733.2163.camel@palm.tree.com> References: <1095468747.31297.241.camel@palm.tree.com> <1096477932.3733.1471.camel@palm.tree.com> <1096489576.3733.1868.camel@palm.tree.com> <200409291652.29990.jhb@FreeBSD.org> <1096496057.3733.2163.camel@palm.tree.com>
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On Wed, 2004-09-29 at 18:14, Stephan Uphoff wrote: > I was looking at the MUTEX_WAKE_ALL undefined case when I used the > critical section for turnstile_claim(). > However there are bigger problems with MUTEX_WAKE_ALL undefined > so you are right - the critical section for turnstile_claim is pretty > useless. Arghhh !!! MUTEX_WAKE_ALL is NOT an option in GENERIC. I recall verifying that it is defined twice. Guess I must have looked at the wrong source tree :-( This means yes - we have bigger problems! Example: Thread A holds a mutex x contested by Thread B and C and has priority pri(A). Thread C holds a mutex y and pri(B) < pri(C) Thread A releases the lock wakes thread B but lets C on the turnstile wait queue. An interrupt thread I tries to lock mutex y owned by C. However priority inheritance does not work since B needs to run first to take ownership of the lock. I is blocked :-( This was found using Peter Holm's test and a slight modification of this giant hog detector. (kern_clock.diff) I definitely won't have time to fix kern_mutex.c for the next few days so please add the line: options MUTEX_WAKE_ALL # Needed do not remove to your configuration files. I also had overlooked http://www.holm.cc/stress/log/cons80.html Showing that my patch for kern_switch.c (switch_patch) has a bug. I will send an updated patch later today. Stephan PS: I love the firewire debugging speed!
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