PI mutex support on ARM

5 messages, 4 authors, 2007-07-09 · open the first message on its own page

PI mutex support on ARM

From: Remy Bohmer <hidden>
Date: 2007-07-08 08:25:10

Hello Thomas,

I have build an implementation for the routine
futex_atomic_cmpxchg_inatomic() to make PTHREAD_PRIO_INHERIT mutex
work on ARM.
Compared to other architectures where CPU specific assembler is used,
it is probably not the most optimal implementation possible, but I
tested it successfully on a Atmel AT91RM9200 core, and it could work
on other (UP) architectures as well.

What do you think of it?
Or do you know a better solution?

Kind Regards,

Remy

Re: PI mutex support on ARM

From: Ingo Molnar <hidden>
Date: 2007-07-08 09:58:56

* Remy Bohmer [off-list ref] wrote:

quoted hunk

--- linux-2.6.21.orig/include/asm/futex.h	2007-04-26 05:08:32.000000000 +0200

patch format problem: never diff the asm/ files, diff the asm-arm/ 
files.

quoted hunk

+	local_irq_save(flags);
+
+	err = get_user(uval, uaddr);

is it safe to do a get_user() with irqs off?

quoted hunk

+	if (err)
+	{
+		local_irq_restore(flags);
+		 return -EFAULT;
+	}

(style problems. Use scripts/checkpatch.pl to verify your patches.)

+	local_irq_restore(flags);

is this method of atomic ops SMP-safe?

	Ingo

Re: PI mutex support on ARM

From: Remy Bohmer <hidden>
Date: 2007-07-08 20:17:52

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

Re: PI mutex support on ARM

From: Matthieu CASTET <hidden>
Date: 2007-07-09 07:25:06

Hi,

Remy Bohmer <l.pinguin <at> gmail.com> writes:

Hello Thomas,

I have build an implementation for the routine
futex_atomic_cmpxchg_inatomic() to make PTHREAD_PRIO_INHERIT mutex
work on ARM.
Compared to other architectures where CPU specific assembler is used,
it is probably not the most optimal implementation possible, but I
tested it successfully on a Atmel AT91RM9200 core, and it could work
on other (UP) architectures as well.

What do you think of it?
Or do you know a better solution?

May be you could have a look at __kuser_cmpxchg (arch/arm/kernel/entry-armv.S).
There stuff for smp for armv6 and newer.
For armv5 and older, maybe masking interrupt is the best solution.


But I believe you should CC arm linux mailling list. You should find more arm
expert :)


Matthieu

Re: PI mutex support on ARM

From: Arjan van de Ven <hidden>
Date: 2007-07-09 14:46:44

On Sun, 2007-07-08 at 22:17 +0200, Remy Bohmer wrote:

Hello Ingo,

quoted

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 ...

quoted

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?

if get_user() isn't allowed with irq's off (and in general it's not,
maybe arm is special) then it also isn't allowed with spinlocks held..

`h`	back out one level
`j`	next message in thread
`k`	previous message in thread
`l`	drill in
`Esc`	close help / fold thread tree
`?`	toggle this help