linux-kernel - [PATCH] mn10300: select generic atomic64

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Date:	Tue, 14 Aug 2012 23:17:04 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Koichi Yasutake <yasutake.koichi@...panasonic.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-am33-list@...hat.com, linux-kernel@...r.kernel.org
Subject: [PATCH] mn10300: select generic atomic64_t support

Rationals from Eric:

So I just looked a little deeper and it appears architectures that do
not support atomic64_t are broken.

The generic atomic64 support came in 2009 to support the perf subsystem
with the expectation that all architectures would implement atomic64
support.

Furthermore upon inspection of the kernel atomic64_t is used in a fair
number of places beyond the performance counters:

block/blk-cgroup.c
drivers/acpi/apei/
drivers/block/rbd.c
drivers/crypto/nx/nx.h
drivers/gpu/drm/radeon/radeon.h
drivers/infiniband/hw/ipath/
drivers/infiniband/hw/qib/
drivers/staging/octeon/
fs/xfs/
include/linux/perf_event.h
include/net/netfilter/nf_conntrack_acct.h
kernel/events/
kernel/trace/
net/mac80211/key.h
net/rds/

The block control group, infiniband, xfs, crypto, 802.11, netfilter.
Nothing quite so fundamental as fs/namespace.c but definitely in
multiplatform-code that should work, and is already broken on those
architecutres.

Looking at the implementation of atomic64_add_return in lib/atomic64.c
the code looks as efficient as these kinds of things get.

Which leads me to the conclusion that we need atomic64 support on all
architectures.

CC: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Fengguang Wu <fengguang.wu@...el.com>
---
 arch/mn10300/Kconfig |    1 +
 1 file changed, 1 insertion(+)

--- linux.orig/arch/mn10300/Kconfig	2012-08-03 15:36:21.391560778 +0800
+++ linux/arch/mn10300/Kconfig	2012-08-14 22:53:14.751795832 +0800
@@ -8,6 +8,7 @@ config MN10300
 	select HAVE_ARCH_KGDB
 	select HAVE_NMI_WATCHDOG if MN10300_WD_TIMER
 	select GENERIC_CLOCKEVENTS
+	select GENERIC_ATOMIC64

 config AM33_2
 	def_bool n
--
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