linux-kernel - Re: [PATCH 0/2] jump label: 2.6.38 updates

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Message-ID: <BLU0-SMTP7346C4AACBF72B473334996D00@phx.gbl>
Date:	Mon, 14 Feb 2011 18:34:05 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	David Miller <davem@...emloft.net>
CC:	matt@...sole-pimps.org, rostedt@...dmis.org, peterz@...radead.org,
	will.newton@...il.com, jbaron@...hat.com, hpa@...or.com,
	mingo@...e.hu, tglx@...utronix.de, andi@...stfloor.org,
	roland@...hat.com, rth@...hat.com, masami.hiramatsu.pt@...achi.com,
	fweisbec@...il.com, avi@...hat.com, sam@...nborg.org,
	ddaney@...iumnetworks.com, michael@...erman.id.au,
	linux-kernel@...r.kernel.org, vapier@...too.org,
	cmetcalf@...era.com, dhowells@...hat.com, schwidefsky@...ibm.com,
	heiko.carstens@...ibm.com, benh@...nel.crashing.org,
	paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 0/2] jump label: 2.6.38 updates

* David Miller (davem@...emloft.net) wrote:
> From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> Date: Mon, 14 Feb 2011 18:03:01 -0500
> 
> > If this is true, then we have bugs in lots of xchg/cmpxchg users (which
> > do not reside in atomic.h), e.g.:
> > 
> > fs/fs_struct.c:
> > int current_umask(void)
> > {
> >         return current->fs->umask;
> > }
> > EXPORT_SYMBOL(current_umask);
> > 
> > kernel/sys.c:
> > SYSCALL_DEFINE1(umask, int, mask)
> > {
> >         mask = xchg(&current->fs->umask, mask & S_IRWXUGO);
> >         return mask;
> > }
> > 
> > The solution to this would be to force all xchg/cmpxchg users to swap to
> > atomic.h variables, which would force the ll semantic on read. But I'd
> > really like to see where this is documented first -- or which PowerPC
> > engineer we should talk to.
> 
> We can't wholesale to atomic_t because we do this on variables of
> all sizes, not just 32-bit ones.
> 
> We do them on pointers in the networking for example.

We have atomic_long_t for this, but yeah, it would kind of suck to have
to create

union {
	atomic_long_t atomic;
	void *ptr;
}

all around the place. Let's see if we can get to know which PowerPC
processor family all this fuss is about, and where this rumour
originates from.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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