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Subject: Re: [RFC][PATCH] spinlock: Kill spin_unlock_wait()
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Chris Mason <chris.mason@oracle.com>,
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        Tejun Heo <tj@kernel.org>
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Date: Thu, 06 Jan 2011 19:26:35 +0100
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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.