ACCESS_ONCE does not work reliably on non-scalar types. For
example gcc 4.6 and 4.7 might remove the volatile tag for such
accesses during the SRA (scalar replacement of aggregates) step
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)
Change the spinlock code to access the union members with
ACCESS_ONCE to avoid this problem.
Signed-off-by: Christian Borntraeger <borntrae...@de.ibm.com>
---
arch/x86/include/asm/spinlock.h | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 9295016..168eb59 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -8,6 +8,7 @@
#include <linux/compiler.h>
#include <asm/paravirt.h>
#include <asm/bitops.h>
+#include <asm/spinlock_types.h>
/*
* Your basic SMP spinlocks, allowing only a single CPU anywhere
@@ -105,7 +106,7 @@ static __always_inline int
arch_spin_trylock(arch_spinlock_t *lock)
{
arch_spinlock_t old, new;
- old.tickets = ACCESS_ONCE(lock->tickets);
+ old.head_tail = ACCESS_ONCE(lock->head_tail);
if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))
return 0;
@@ -162,16 +163,19 @@ static __always_inline void
arch_spin_unlock(arch_spinlock_t *lock)
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
- struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
+ arch_spinlock_t tmp = {};
- return tmp.tail != tmp.head;
+ tmp.head_tail =ACCESS_ONCE(lock->head_tail);
+ return tmp.tickets.tail != tmp.tickets.head;
}
static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
- struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
+ arch_spinlock_t tmp = {};
+
+ tmp.head_tail = ACCESS_ONCE(lock->head_tail);
+ return (__ticket_t)(tmp.tickets.tail - tmp.tickets.head) >
TICKET_LOCK_INC;
- return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;
}
#define arch_spin_is_contended arch_spin_is_contended
--
1.9.3
--
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