linux-kernel - Re: [PATCH][RFC]: mutex: adaptive spin

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Date:	Tue, 6 Jan 2009 17:56:15 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Matthew Wilcox <matthew@....cx>,
	Andi Kleen <andi@...stfloor.org>,
	Chris Mason <chris.mason@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH][RFC]: mutex: adaptive spin


* Ingo Molnar <mingo@...e.hu> wrote:

> One thought:
> 
> BUG_ON()'s do_exit() shows a slightly misleading failure pattern to 
> users: instead of a 'hanging' task, we'd get a misbehaving app due to 
> one of its tasks exiting spuriously. It can even go completely unnoticed 
> [users dont look at kernel logs normally] - while a hanging task 
> generally does get noticed. (because there's no progress in processing)
> 
> So instead of the BUG_ON() we could emit a WARN_ONCE() perhaps, plus not 
> do any spinning and just block - resulting in an uninterruptible task 
> (that the user will probably notice) and a scary message in the syslog? 
> [all in the slowpath]

And we'd strictly do an uninterruptible sleep here, unconditionally: even 
if this is within mutex_lock_interruptible() - we dont want a Ctrl-C or a 
SIGKILL to allow to 'break out' the app from the deadlock.

	Ingo
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