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

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Date:	Tue, 14 Aug 2007 15:06:12 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	"Chris Snook" <csnook@...hat.com>, <clameter@....com>
Cc:	<linux-arch@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	<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

>> 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

> Do you get any warnings other than those two?

That looks like six, not two.  But that's the whole list.

>IIRC, when you applied a version which used macros instead, there was no change. 
>  It would seem that inlining changed the optimization behavior of the compiler. 
>  If you turn down the optimization level, do the macro and inline versions look 
>  the same, or at least more similar?

I re-tried the macros ... the three warnings from mm/slub.c all result in
broken code ... and quite rightly too, they all come from code that does:

	atomic_read(&n->nr_slabs)

But the nr_slabs field is an atomic_long_t, so we shouldn't be using
atomic_read().  I didn't spot these last time around because I was using
slab, not slub for the previous build.

I think that I'll run into other build issues if I turn down the
optimization level (there are lots of places where the kernel relies
on optimizing away impossible cases in switch statements.

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

-Tony
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