From: Olof Johansson <olof@lixom•net>
To: Becky Bruce <becky.bruce@freescale•com>
Cc: linuxppc-dev@ozlabs•org
Subject: Re: [PATCH] Avoid unpaired stwcx. on some processors
Date: Fri, 9 Nov 2007 18:18:00 -0600 [thread overview]
Message-ID: <20071110001759.GA21447@lixom.net> (raw)
In-Reply-To: <260A8045-7F86-46EC-9242-08BC2669890F@freescale.com>
On Fri, Nov 09, 2007 at 05:52:30PM -0600, Becky Bruce wrote:
> I don't think so. It's not plain old dangling stwcx that's the
> problem. It's dangling stwcx when the reservation is held to another
> address.
Gack, I misread the description. My bad.
> The lwarx that I've added prevents the normally dangling
> stwcx. in the context switch/syscall path from meeting this
> condition. Any process that gets swapped in and executes stwcx.
> first thing is fine, because the reservation was previously cleared
> by the stwcx. in the context switch path.
>
> BTW, I think you're missing a key point here, which is this:
> Architecturally, there is a single reservation per core. On e600 and
> other parts, the stwcx. does *not* take the address into account for
> success. If you stwcx, and the reservation is held, it succeeds
> regardless of the address. Fun, no? That's one of the reasons
> it's so important that the kernel have the dummy stwcx. in place.
>
> Does that make sense?
Yep, it does, doesn't seem to be a better way to work around it.
-Olof
next prev parent reply other threads:[~2007-11-10 0:17 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-09 22:08 [PATCH] Avoid unpaired stwcx. on some processors Becky Bruce
2007-11-09 23:19 ` Olof Johansson
2007-11-09 23:52 ` Becky Bruce
2007-11-10 0:18 ` Olof Johansson [this message]
2007-11-11 4:46 ` Benjamin Herrenschmidt
2007-11-11 7:14 ` Olof Johansson
-- strict thread matches above, loose matches on Subject: below --
2007-11-09 22:17 Becky Bruce
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