linux-kernel - Re: PI mutex support on ARM

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Date:	Sun, 8 Jul 2007 22:17:40 +0200
From:	"Remy Bohmer" <l.pinguin@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Thomas Gleixner" <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: PI mutex support on ARM

Hello Ingo,

> patch format problem: never diff the asm/ files, diff the asm-arm/ files.
Yeah, of course, I know, I believe I made a real mess of this one ...

> is it safe to do a get_user() with irqs off?
rhetorical question ;-))
I was wondering, Is it safe to use a normal spinlock here, like this?

------- 8-< -------------
	spin_lock(&futex_lock);

	err = get_user(uval, uaddr);
	if ((!err) && (uval == oldval))
		err = put_user(newval, uaddr);

	spin_unlock(&futex_lock);
------- 8-< -------------

> is this method of atomic ops SMP-safe?
another rhetorical question ;-))
Nope, I already knew that, that why I mentioned that it probably only
worked on UP...

Remy
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