Message-ID: <BLU0-SMTP7346C4AACBF72B473334996D00@phx.gbl>
Date: Mon, 14 Feb 2011 18:34:05 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
To: David Miller <davem@davemloft.net>
CC: matt@console-pimps.org, rostedt@goodmis.org, peterz@infradead.org,
        will.newton@gmail.com, jbaron@redhat.com, hpa@zytor.com, mingo@elte.hu,
        tglx@linutronix.de, andi@firstfloor.org, roland@redhat.com,
        rth@redhat.com, masami.hiramatsu.pt@hitachi.com, fweisbec@gmail.com,
        avi@redhat.com, sam@ravnborg.org, ddaney@caviumnetworks.com,
        michael@ellerman.id.au, linux-kernel@vger.kernel.org,
        vapier@gentoo.org, cmetcalf@tilera.com, dhowells@redhat.com,
        schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com,
        benh@kernel.crashing.org, paulmck@linux.vnet.ibm.com
Subject: Re: [PATCH 0/2] jump label: 2.6.38 updates
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* David Miller (davem@davemloft.net) wrote:
> From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.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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