From: Ingo Molnar <mingo@elte.hu>
To: Linus Torvalds <torvalds@osdl.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@osdl.org>,
Arjan van de Ven <arjanv@infradead.org>,
Jes Sorensen <jes@trained-monkey.org>,
Zwane Mwaikambo <zwane@arm.linux.org.uk>,
Oleg Nesterov <oleg@tv-sign.ru>,
David Howells <dhowells@redhat.com>,
Alan Cox <alan@lxorguk.ukuu.org.uk>,
Benjamin LaHaise <bcrl@kvack.org>,
Steven Rostedt <rostedt@goodmis.org>,
Christoph Hellwig <hch@infradead.org>, Andi Kleen <ak@suse.de>,
Russell King <rmk+lkml@arm.linux.org.uk>,
Nicolas Pitre <nico@cam.org>
Subject: Re: [patch 3/8] mutex subsystem, add atomic_*_call_if_*() to i386
Date: Wed, 21 Dec 2005 21:01:01 +0100 [thread overview]
Message-ID: <20051221200101.GA18565@elte.hu> (raw)
In-Reply-To: <Pine.LNX.4.64.0512211054450.4827@g5.osdl.org>
* Linus Torvalds <torvalds@osdl.org> wrote:
> > Umm. This asm is broken. It doesn't mark %eax as changed, so this is only
> > reliable if the function you call is
> >
> > - a "fastcall" one
> > - always returns as its return value the pointer to the atomic count
> >
> > which is not true (you verify that it's a fastcall, but it's of type
> > "void").
>
> Actually (and re-reading the email I sent that wasn't obvious at all),
> my _preferred_ fix is to literally force the use of the above kind of
> function: not save/restore %eax at all, but just say that any function
> that is called by the magic "atomic_*_call_if()" needs to always
> return the argument it gets as its return value too.
>
> That allows the caller to not even have to care. And the callee
> obviously already _has_ that value, so it might as well return it (and
> in the best case it's not going to add any cost at all, either to the
> caller or the callee).
>
> So you might opt to keep the asm the same, just change the calling
> conventions.
ok, i've added this fix, thanks. Right now we dont do anything after
those functions (that's probably how the bug never showed up), but at
least one interim stage i tried to use the call_if functions at other
places too, so the potential is there.
Ingo
next prev parent reply other threads:[~2005-12-21 20:01 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-21 15:54 [patch 3/8] mutex subsystem, add atomic_*_call_if_*() to i386 Ingo Molnar
2005-12-21 18:54 ` Linus Torvalds
2005-12-21 18:57 ` Linus Torvalds
2005-12-21 20:01 ` Ingo Molnar [this message]
2005-12-21 20:32 ` Daniel Jacobowitz
2005-12-21 20:54 ` Nicolas Pitre
2005-12-22 9:18 ` Keith Owens
2005-12-21 19:47 ` Ingo Molnar
2005-12-21 22:40 ` Linus Torvalds
2005-12-21 22:37 Ingo Molnar
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