Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 4f9d1382 authored by Christian Borntraeger's avatar Christian Borntraeger
Browse files

x86/spinlock: Replace ACCESS_ONCE with READ_ONCE 

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 replace ACCESS_ONCE with READ_ONCE.

Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Acked-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent e37c6982

arch/x86/include/asm/spinlock.h

+4 −4
Original line number Original line Diff line number Diff line
@@ -92,7 +92,7 @@ static __always_inline void arch_spin_lock(arch_spinlock_t *lock) 
		unsigned count = SPIN_THRESHOLD;

		unsigned count = SPIN_THRESHOLD;





		do {

		do {

			if (ACCESS_ONCE(lock->tickets.head) == inc.tail)

			if (READ_ONCE(lock->tickets.head) == inc.tail)

				goto out;

				goto out;

			cpu_relax();

			cpu_relax();

		} while (--count);

		} while (--count);
@@ -105,7 +105,7 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock) 
{

{

	arch_spinlock_t old, new;

	arch_spinlock_t old, new;





	old.tickets = ACCESS_ONCE(lock->tickets);

	old.tickets = READ_ONCE(lock->tickets);

	if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))

	if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))

		return 0;

		return 0;
@@ -162,14 +162,14 @@ static __always_inline void arch_spin_unlock(arch_spinlock_t *lock) 




static inline int arch_spin_is_locked(arch_spinlock_t *lock)

static inline int arch_spin_is_locked(arch_spinlock_t *lock)

{

{

	struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);

	struct __raw_tickets tmp = READ_ONCE(lock->tickets);





	return tmp.tail != tmp.head;

	return tmp.tail != tmp.head;

}

}





static inline int arch_spin_is_contended(arch_spinlock_t *lock)

static inline int arch_spin_is_contended(arch_spinlock_t *lock)

{

{

	struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);

	struct __raw_tickets tmp = READ_ONCE(lock->tickets);





	return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;

	return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;

}

}