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

[Matthew Wilcox <matthew@wil.cx>]

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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"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
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