Messages in this thread | | | Date | Mon, 11 Apr 2005 17:27:41 -0700 | Subject | Re: [PATCH] Priority Lists for the RT mutex | From | Bill Huey (hui) <> |
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On Mon, Apr 11, 2005 at 04:28:25PM -0700, Perez-Gonzalez, Inaky wrote: > >From: Bill Huey (hui) [mailto:bhuey@lnxw.com] ... > API than once upon a time was made multithreaded by just adding > a bunch of pthread_mutex_[un]lock() at the API entry point... > without realizing that some of the top level API calls also > called other top level API calls, so they'd deadlock.
Oh crap.
> Quick fix: the usual. Enable deadlock detection and if it > returns deadlock, assume it is locked already and proceed (or > do a recursive mutex, or a trylock).
You have to be joking me ? geez. ... > It is certainly something to explore, but I'd better drive your > way than do it. It's cleaner. Hides implementation details. > > I agree, but it doesn't work that well when talking about legacy > systems...that's the problem.
Yeah, ok, I understand what's going on now. There isn't a notion of projecting priority across into the Unix/Linux kernel traditionally which is why it seemed so bizarre.
> Sure--and because most was for legacy reasons that adhered to > POSIX strictly, it was very simple: we need POSIX this, that and > that (PI, proper adherence to scheduler policy wake up/rt-behaviour, > deadlock detection, etc).
Some of this stuff sounds like recursive locking. Would this be a better expression to solve the "top level API locking" problem you're referring to ?
> Fortunately in those areas POSIX is not too gray; code to the book. > Deal.
I would think that there will have to be a graph discontinuity between user/kernel spaces at kernel entry and exit for the deadlock detector. Can't say about issues at fork time, but I would expect that those objects would have to be destroyed when the process exits.
The current RT (Ingo's) lock isn't recursive nor is the deadlock detector the last time I looked. Do think that this is a problem for legacy apps if it gets overload for being the userspace futex as well ? (assuming I'm understanding all of this correctly)
> Of course, selling it to the lkml is another story.
I would think that pushing as much of this into userspace would make the kernel hooks for it more acceptable. Don't know.
/me thinks more
bill
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