Messages in this thread | | | Subject | Re: [PATCH 3/3] futex: fix miss ordered wakeups | From | Daniel Walker <> | Date | Sat, 24 May 2008 10:24:20 -0700 |
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On Sat, 2008-05-24 at 19:03 +0200, Thomas Gleixner wrote: > On Sat, 24 May 2008, Daniel Walker wrote: > > On Sat, 2008-05-24 at 10:55 +0200, Thomas Gleixner wrote: > > > > > Normal futexes have no ordering guarantees at all. There is no > > > mechanism to prevent lock stealing from lower priority tasks. So why > > > should we care about the once a year case, where a sleepers priority > > > is modified ? > > > > Lock stealing? > > Do you have the faintest idea how the futex code works at all ? There > is no guarantee that the task which is woken up first gets the futex.
Thomas if you want to be abusive, talk to someone else.
> A) A task on another CPU can get it independent of its priority > B) In case of multiple waiters wakeup there is no guarantee either
This is how I would imagine the pre-plist code would work.
> > > If you need ordering guarantees then use PI futexes. > > > > There are degree's of overhead with each step.. Someone may not need or > > want priority inheritance. > > Then there is no need to add this artifical "correctness" at all.
huh?
> > > There are more issues vs. pi futexes as well. The simple case of > > > futex_wait() vs. futex_adjust_waiters will just upset lockdep, but > > > there are real dealocks vs. unqueue_me_pi waiting. > > > > You mean the lock ordering would cause the deadlock vs. unqueue_me_pi , > > or are you talking about something else? > > Do I write Chinese or what ?
I guess so ..
Daniel
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