linux-kernel - RE: [PATCH 10/23] make atomic_read() and atomic

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Date:	Tue, 14 Aug 2007 11:27:35 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	"Chris Snook" <csnook@...hat.com>, <linux-arch@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	<akpm@...ux-foundation.org>, <paulmck@...ux.vnet.ibm.com>,
	"Segher Boessenkool" <segher@...nel.crashing.org>,
	"Chris Friesen" <cfriesen@...tel.com>,
	"Robert P. J. Day" <rpjday@...dspring.com>
Subject: RE: [PATCH 10/23] make atomic_read() and atomic_set() behavior consistent on ia64

> Use volatile consistently in atomic.h on ia64.
> This will do weird things without Andreas Schwab's fix:
> http://lkml.org/lkml/2007/8/10/410

The build is very noisy with the inline versions of atomic_{read,set}
and their 64-bit siblings.  Here are the prime culprits (some of them
repeat >100 times).

include/linux/skbuff.h:521: warning: passing arg 1 of `atomic_read' discards qualifiers from pointer target type
include/net/sock.h:1244: warning: passing arg 1 of `atomic_read' discards qualifiers from pointer target type
include/net/tcp.h:958: warning: passing arg 1 of `atomic_read' discards qualifiers from pointer target type
mm/slub.c:3115: warning: passing arg 1 of `atomic_read' from incompatible pointer type
mm/slub.c:3250: warning: passing arg 1 of `atomic_read' from incompatible pointer type
mm/slub.c:3286: warning: passing arg 1 of `atomic_read' from incompatible pointer type

The inline versions also result in some structural changes in
the object file that make it difficult to compare with the
original.  Text size is 96 bytes smaller ... but even after
I use sed(1) to exclude the most obvious instructions that
differ, I still find big blocks of code with changes.  Perhaps
even more surprising there are entire functions that are
optimized out in either the 'before' or 'after' binary.
E.g. lookup_pi_state() was optimized away (or completely
inlined?) before this patch, but the function appears as
standalone in the 'after' version.  The reverse is true for
fixup_pi_state_owner().

The binary does boot ... but I haven't run any tests to see whether
there are any problems.

-Tony
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