Re: [RFC, PATCH] locks: remove posix deadlock detection

Matthew Wilcox
2007-10-28T23:31:32Z

On Sun, Oct 28, 2007 at 11:55:52PM +0100, Jiri Kosina wrote:
> On Sun, 28 Oct 2007, Matthew Wilcox wrote:
>
> > Bzzt. You get a false deadlock with multiple threads like so:
> > Thread A of task B takes lock 1
> > Thread C of task D takes lock 2
> > Thread C of task D blocks on lock 1
> > Thread E of task B blocks on lock 2
>
> A potential for deadlock occurs if a process controlling a locked
> region is put to sleep by attempting to lock another process'
> locked region. If the system detects that sleeping until a locked
> region is unlocked would cause a deadlock, fcntl() shall fail with
> an [EDEADLK] error.
>
> This is what POSIX says [1], even after being modified with respect to
> POSIX Threads Extension, right?
>
> So it doesn't deal with threads at all, just processess are taken into
> account. Probably for a reason :)

Did you have a concrete suggestion, or are you just quoting the spec?

The problem is that it's nonsense -- processes don't sleep, threads do.
I think the key is "would deadlock", not "might deadlock". Our current
behaviour is clearly in violation of SuSv3.

--
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