linux-kernel - RE: [PATCH 9/24] make atomic_read() behave consistently on ia64

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Date:	Fri, 10 Aug 2007 15:33:27 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	"Andreas Schwab" <schwab@...e.de>
Cc:	"Chris Snook" <csnook@...hat.com>, <linux-kernel@...r.kernel.org>,
	<linux-arch@...r.kernel.org>, <torvalds@...ux-foundation.org>,
	<netdev@...r.kernel.org>, <akpm@...ux-foundation.org>,
	<ak@...e.de>, <heiko.carstens@...ibm.com>, <davem@...emloft.net>,
	<schwidefsky@...ibm.com>, <wensong@...ux-vs.org>,
	<horms@...ge.net.au>, <wjiang@...ilience.com>,
	<cfriesen@...tel.com>, <zlynx@....org>, <rpjday@...dspring.com>,
	<jesper.juhl@...il.com>
Subject: RE: [PATCH 9/24] make atomic_read() behave consistently on ia64

> Use atomic64_read to read an atomic64_t.

Thanks Andreas!

Chris: This bug is why the 8-byte loads got changed to 4-byte + sign-extend
by your change to atomic_read().

With this applied together with shuffling the volatile from the
declaration to the usage (in both atomic_read() and atomic_set()
the generated code *almost* reverts to the original.

There are some differences where ld4 have turned into ld8 though.
Are these bugs in the use of atomic_add() and atomic_sub().  E.g.
the first of these changes is in: ipc/msg.c:freeque() where we have:

	atomic_sub(msg->q_cbytes, &msg_bytes);

Now the type of msg->q_cbytes is "unsigned long" ... so it seems a
poor idea to subtract such a large typed object from "msg_bytes"
which is a mere slip of an atomic_t.

Or is there some other type-wrangling that needs to happen in
include/asm-ia64/atomic.h?  There are a total of nineteen of
these ld4->ld8 transforms.

-Tony
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