linux-kernel - Re: [cpuops cmpxchg double V1 2/4] x86: this_cpu_cmpxchg

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Date:	Wed, 15 Dec 2010 10:20:53 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Tejun Heo <tj@...nel.org>, akpm@...ux-foundation.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [cpuops cmpxchg double V1 2/4] x86: this_cpu_cmpxchg_double()
 support

Better comments:

Subject: Fixup comments for cmpxchg16b_cpuops_emu

Indicate that the sematics are not fullly atomic but just per cpu atomic.

Signed-off-by: Christoph Lameter <cl@...ux.com>

---
 arch/x86/lib/cmpxchg16b_emu.S |    4 ++++
 1 file changed, 4 insertions(+)

Index: linux-2.6/arch/x86/lib/cmpxchg16b_emu.S
===================================================================
--- linux-2.6.orig/arch/x86/lib/cmpxchg16b_emu.S	2010-12-15 10:18:18.000000000 -0600
+++ linux-2.6/arch/x86/lib/cmpxchg16b_emu.S	2010-12-15 10:19:11.000000000 -0600
@@ -30,6 +30,10 @@ CFI_STARTPROC
 # Emulate 'cmpxchg16b %gs:(%rsi)' except we return the result in
 # al not via the ZF. Caller will access al to get result.
 #
+# Note that this is only useful for a cpuops operation. Meaning that we
+# do *not* have a fully atomic operation but just an operation that is
+# *atomic* on a single cpu (as provided by the this_cpu_xx class of macros)
+#
 cmpxchg16b_cpuops_emu:
 	pushf
 	cli

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