linux-kernel - Re: [RFC][PATCH] spinlock: Kill spin_unlock

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Date:	Thu, 06 Jan 2011 19:26:35 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Nick Piggin <npiggin@...nel.dk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Mason <chris.mason@...cle.com>,
	Frank Rowand <frank.rowand@...sony.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>,
	Oleg Nesterov <oleg@...hat.com>, Paul Turner <pjt@...gle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Yong Zhang <yong.zhang0@...il.com>,
	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	Jeff Garzik <jeff@...zik.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC][PATCH] spinlock: Kill spin_unlock_wait()

On Thu, 2011-01-06 at 21:38 +1100, Nick Piggin wrote:
> I can't see how the usage in libata could be right. If we're waiting
> for some modifications inside the critical section, then it seems we
> could load some shared data before the lock is actually released, on
> an architecture which does load/load reordering. At best it needs some
> good comments and perhaps a barrier or two.
> 
> The spin_unlock_wait in do_exit seems like it shouldn't be needed --
> exit_pi_state_list takes the pi_lock after the task has died anyway,
> so I can't see what the problem would be. Removing the call (and
> perhaps put a BUG_ON(!(curr->flags & PF_EXITING)) in exit_pi_state_list
> would do the same thing, avoid the barrier, and localize fuxtex exit
> protocol to futex.c. 

Jeff, Tejun, could you look at the ata-eh thing, then I'll put sorting
through the futex thing on my todo list.
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