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SubjectRE: Fix unlock_buffer() to work the same way as bit_unlock()
On Tue, 28 Mar 2006, Chen, Kenneth W wrote:

> Why not make unlock_buffer use test_and_clear_bit()? Utilizing it's implied
> full memory fence and throw away the return value? OK, OK, this is obscured.
> Then introduce clear_bit_memory_fence API or some sort.

Only for IA64's sake? Better clean up the bitops as you suggested earlier.
The open ended acquires there leaves a weird feeling.

Something like this? (builds fine not tested yet)



Fix up the bitops for ia64.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.16/include/asm-ia64/bitops.h
===================================================================
--- linux-2.6.16.orig/include/asm-ia64/bitops.h 2006-03-19 21:53:29.000000000 -0800
+++ linux-2.6.16/include/asm-ia64/bitops.h 2006-03-28 16:35:51.000000000 -0800
@@ -38,13 +38,14 @@ set_bit (int nr, volatile void *addr)
volatile __u32 *m;
CMPXCHG_BUGCHECK_DECL

+ /* Volatile load = acq */
m = (volatile __u32 *) addr + (nr >> 5);
bit = 1 << (nr & 31);
do {
CMPXCHG_BUGCHECK(m);
old = *m;
new = old | bit;
- } while (cmpxchg_acq(m, old, new) != old);
+ } while (cmpxchg_rel(m, old, new) != old);
}

/**
@@ -65,7 +66,7 @@ __set_bit (int nr, volatile void *addr)
/*
* clear_bit() has "acquire" semantics.
*/
-#define smp_mb__before_clear_bit() smp_mb()
+#define smp_mb__before_clear_bit() do { /* skip */; } while (0)
#define smp_mb__after_clear_bit() do { /* skip */; } while (0)

/**
@@ -85,13 +86,14 @@ clear_bit (int nr, volatile void *addr)
volatile __u32 *m;
CMPXCHG_BUGCHECK_DECL

+ /* Volatile load = acq */
m = (volatile __u32 *) addr + (nr >> 5);
mask = ~(1 << (nr & 31));
do {
CMPXCHG_BUGCHECK(m);
old = *m;
new = old & mask;
- } while (cmpxchg_acq(m, old, new) != old);
+ } while (cmpxchg_rel(m, old, new) != old);
}

/**
@@ -121,13 +123,14 @@ change_bit (int nr, volatile void *addr)
volatile __u32 *m;
CMPXCHG_BUGCHECK_DECL

+ /* Volatile load = acq */
m = (volatile __u32 *) addr + (nr >> 5);
bit = (1 << (nr & 31));
do {
CMPXCHG_BUGCHECK(m);
old = *m;
new = old ^ bit;
- } while (cmpxchg_acq(m, old, new) != old);
+ } while (cmpxchg_rel(m, old, new) != old);
}

/**
@@ -160,13 +163,14 @@ test_and_set_bit (int nr, volatile void
volatile __u32 *m;
CMPXCHG_BUGCHECK_DECL

+ /* Volatile load = acq */
m = (volatile __u32 *) addr + (nr >> 5);
bit = 1 << (nr & 31);
do {
CMPXCHG_BUGCHECK(m);
old = *m;
new = old | bit;
- } while (cmpxchg_acq(m, old, new) != old);
+ } while (cmpxchg_rel(m, old, new) != old);
return (old & bit) != 0;
}

@@ -205,13 +209,14 @@ test_and_clear_bit (int nr, volatile voi
volatile __u32 *m;
CMPXCHG_BUGCHECK_DECL

+ /* Volatile load = acq */
m = (volatile __u32 *) addr + (nr >> 5);
mask = ~(1 << (nr & 31));
do {
CMPXCHG_BUGCHECK(m);
old = *m;
new = old & mask;
- } while (cmpxchg_acq(m, old, new) != old);
+ } while (cmpxchg_rel(m, old, new) != old);
return (old & ~mask) != 0;
}

-
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