On Sat, 2005-12-17 at 16:43 -0700, Matthew Wilcox wrote: > On Fri, Dec 16, 2005 at 11:34:03PM -0800, Linus Torvalds wrote: > > I really can't think of any blocking kernel lock where priority > > inheritance would make _any_ sense at all. Please give me an example. > > I have a better example of something we currently get wrong that I > haven't heard any RT person worry about yet. If two tasks are sleeping > on the same semaphore, the one to be woken up will be the first one to > wait for it, not the highest-priority task. > > Obviously, this was introduced by the wake-one semantics. But how to > fix it? Should we scan the entire queue looking for the best task to > wake? Should we try to maintain the wait list in priority order? Or > should we just not care? Should we document that we don't care? ;-)
It's well known that this is a problem: http://developer.osdl.org/dev/robustmutexes/src/fusyn.hg/Documentation/fusyn/fusyn-why.txt Lee
