RE: Fix unlock_buffer() to work the same way as bit_unlock()

From: Christoph Lameter <clameter_at_sgi.com>
Date: 2006-03-29 11:47:15
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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Received on Wed Mar 29 11:47:55 2006

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