Subject: Re: [PATCH] Document Linux's memory barriers
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Paul Mackerras <paulus@samba.org>
Cc: Duncan Sands <duncan.sands@math.u-psud.fr>,
       David Howells <dhowells@redhat.com>, akpm@osdl.org,
       linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
       torvalds@osdl.org, mingo@redhat.com, linuxppc64-dev@ozlabs.org
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Date: Wed, 08 Mar 2006 22:42:29 +0000
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On Iau, 2006-03-09 at 09:06 +1100, Paul Mackerras wrote:
> I'd be interested to know what the C standard says about whether the
> compiler can reorder writes that may be visible to a signal handler.
> An interrupt handler in the kernel is logically equivalent to a signal
> handler in normal C code.

The C standard doesn't have much to say. POSIX has a lot to say and yes
it can do this. You do need volatile or store barriers in signal touched
code quite often, or for that matter locks

POSIX/SuS also has stuff to say about what functions are signal safe and
what is not allowed.

Alan

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