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Date: Thu, 7 Mar 2002 00:48:21 -0800
From: Richard Henderson <rth@twiddle.net>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: torvalds@transmeta.com, matthew@hairy.beasts.org, bcrl@redhat.com,
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Subject: Re: [PATCH] Fast Userspace Mutexes III.
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In-Reply-To: <20020307143947.000f51dd.rusty@rustcorp.com.au>; from rusty@rustcorp.com.au on Thu, Mar 07, 2002 at 02:39:47PM +1100
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On Thu, Mar 07, 2002 at 02:39:47PM +1100, Rusty Russell wrote:
> But since the real problem here is "lock held forever", so I don't care.

No, "lock held forever" merely makes the example trivial.  
"Lock held for a while" is the real problem.

> > You really do need that cmpxchg loop.
> 
> Well, not decrementing if count < 0 already also works

How, exactly, are you planning on doing that atomically?
Clue: 386 SMP requires an extra spinlock.

> PS. Will Alpha have to do any special magic with the mmap PROT_SEM flag?

No.


r~
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