local_t protection (critical section)
Adds local_enter_save(flags) and local_exit_restore(flags) as primitives to
surround critical sections using local_t types.
On architectures providing fast atomic primitives, this turns into a preempt
disable/enable().
However, on architectures not providing such fast primitives, such as ia64, it
turns into a local irq disable/enable so that we can use *_local primitives that
are non atomic.
This is only the primary work here: made for testing ia64 with cmpxchg_local
(other local_* primitives still use atomic_long_t operations as fallback).
Signed-off-by: Mathieu Desnoyers <[email protected]>
Christoph Lameter <[email protected]>
---
include/asm-generic/local.h | 9 +++++++++
include/asm-i386/local.h | 17 +++++++++++++++++
include/asm-ia64/intrinsics.h | 14 ++++++++++++--
3 files changed, 38 insertions(+), 2 deletions(-)
Index: linux-2.6-lttng/include/asm-generic/local.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-generic/local.h 2007-09-04 15:32:02.000000000 -0400
+++ linux-2.6-lttng/include/asm-generic/local.h 2007-09-05 08:50:47.000000000 -0400
@@ -46,6 +46,15 @@ typedef struct
#define local_add_unless(l, a, u) atomic_long_add_unless((&(l)->a), (a), (u))
#define local_inc_not_zero(l) atomic_long_inc_not_zero(&(l)->a)
+#define local_enter_save(flags) local_irq_save(flags)
+#define local_exit_restore(flags) local_irq_restore(flags)
+#define local_enter() local_irq_disable()
+#define local_exit() local_irq_enable()
+#define local_nest_irq_save(flags) (flags)
+#define local_nest_irq_restore(flags) (flags)
+#define local_nest_irq_disable()
+#define local_nest_irq_enable()
+
/* Non-atomic variants, ie. preemption disabled and won't be touched
* in interrupt, etc. Some archs can optimize this case well. */
#define __local_inc(l) local_set((l), local_read(l) + 1)
Index: linux-2.6-lttng/include/asm-i386/local.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-i386/local.h 2007-09-04 15:28:52.000000000 -0400
+++ linux-2.6-lttng/include/asm-i386/local.h 2007-09-05 08:49:19.000000000 -0400
@@ -194,6 +194,23 @@ static __inline__ long local_sub_return(
})
#define local_inc_not_zero(l) local_add_unless((l), 1, 0)
+#define local_enter_save(flags) \
+ do { \
+ (flags); \
+ preempt_disable(); \
+ } while (0)
+#define local_exit_restore(flags) \
+ do { \
+ (flags); \
+ preempt_enable(); \
+ } while (0)
+#define local_enter() preempt_disable()
+#define local_exit() preempt_enable()
+#define local_nest_irq_save(flags) local_irq_save(flags)
+#define local_nest_irq_restore(flags) local_irq_restore(flags)
+#define local_nest_irq_disable() local_irq_disable()
+#define local_nest_irq_enable() local_irq_enable()
+
/* On x86, these are no better than the atomic variants. */
#define __local_inc(l) local_inc(l)
#define __local_dec(l) local_dec(l)
Index: linux-2.6-lttng/include/asm-ia64/intrinsics.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-ia64/intrinsics.h 2007-09-04 15:47:24.000000000 -0400
+++ linux-2.6-lttng/include/asm-ia64/intrinsics.h 2007-09-04 15:49:41.000000000 -0400
@@ -160,8 +160,18 @@ extern long ia64_cmpxchg_called_with_bad
#define cmpxchg(ptr,o,n) cmpxchg_acq(ptr,o,n)
#define cmpxchg64(ptr,o,n) cmpxchg_acq(ptr,o,n)
-#define cmpxchg_local cmpxchg
-#define cmpxchg64_local cmpxchg64
+/* Must be executed between local_enter/local_exit. */
+static inline void *cmpxchg_local(void **p, void *old, void *new)
+{
+ unsigned long flags;
+ void *before;
+
+ before = *p;
+ if (likely(before == old))
+ *p = new;
+ return before;
+}
+#define cmpxchg64_local cmpxchg_local
#ifdef CONFIG_IA64_DEBUG_CMPXCHG
# define CMPXCHG_BUGCHECK_DECL int _cmpxchg_bugcheck_count = 128;
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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