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

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Date:	Sun, 28 Oct 2007 23:55:52 +0100 (CET)
From:	Jiri Kosina <jikos@...os.cz>
To:	Matthew Wilcox <matthew@....cx>
cc:	Trond Myklebust <trond.myklebust@....uio.no>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	"George G. Davis" <gdavis@...sta.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [RFC, PATCH] locks: remove posix deadlock detection

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 :)

[1] http://www.opengroup.org/onlinepubs/009695399/functions/fcntl.html

-- 
Jiri Kosina
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