From e4f9bfb3feaeaca55cf177dadb7e3313836b10f4 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 4 Feb 2014 20:36:01 +0100 Subject: ia64: Fix up smp_mb__{before,after}_clear_bit() IA64 doesn't actually have acquire/release barriers, its a lie! Add a comment explaining this and fix up the bitop barriers. Signed-off-by: Peter Zijlstra Acked-by: Paul E. McKenney Link: http://lkml.kernel.org/n/tip-akevfh136um9dqvb1ohm55ca@git.kernel.org Cc: Akinobu Mita Cc: Fenghua Yu Cc: Linus Torvalds Cc: Tony Luck Cc: linux-ia64@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- arch/ia64/include/uapi/asm/cmpxchg.h | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'arch/ia64/include/uapi') diff --git a/arch/ia64/include/uapi/asm/cmpxchg.h b/arch/ia64/include/uapi/asm/cmpxchg.h index 4f37dbbb8640..f35109b1d907 100644 --- a/arch/ia64/include/uapi/asm/cmpxchg.h +++ b/arch/ia64/include/uapi/asm/cmpxchg.h @@ -118,6 +118,15 @@ extern long ia64_cmpxchg_called_with_bad_pointer(void); #define cmpxchg_rel(ptr, o, n) \ ia64_cmpxchg(rel, (ptr), (o), (n), sizeof(*(ptr))) +/* + * Worse still - early processor implementations actually just ignored + * the acquire/release and did a full fence all the time. Unfortunately + * this meant a lot of badly written code that used .acq when they really + * wanted .rel became legacy out in the wild - so when we made a cpu + * that strictly did the .acq or .rel ... all that code started breaking - so + * we had to back-pedal and keep the "legacy" behavior of a full fence :-( + */ + /* for compatibility with other platforms: */ #define cmpxchg(ptr, o, n) cmpxchg_acq((ptr), (o), (n)) #define cmpxchg64(ptr, o, n) cmpxchg_acq((ptr), (o), (n)) -- cgit v1.2.3