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ia64: Fix up smp_mb__{before,after}_clear_bit()

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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 <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/n/tip-akevfh136um9dqvb1ohm55ca@git.kernel.org
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-ia64@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2014-02-04 20:36:01 +01:00 committed by Ingo Molnar
parent 81cef0fe19
commit e4f9bfb3fe
2 changed files with 11 additions and 5 deletions
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7
arch/ia64/include/asm/bitops.h
View File

@ -65,11 +65,8 @@ __set_bit (int nr, volatile void *addr)
*((__u32 *) addr + (nr >> 5)) |= (1 << (nr & 31));
}
/*
* clear_bit() has "acquire" semantics.
*/
#define smp_mb__before_clear_bit() smp_mb()
#define smp_mb__after_clear_bit() do { /* skip */; } while (0)
#define smp_mb__before_clear_bit() barrier();
#define smp_mb__after_clear_bit() barrier();
/**
* clear_bit - Clears a bit in memory

9
arch/ia64/include/uapi/asm/cmpxchg.h
View File

@ -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))