diff options
Diffstat (limited to 'kernel/locking/qspinlock.c')
| -rw-r--r-- | kernel/locking/qspinlock.c | 25 |
1 files changed, 16 insertions, 9 deletions
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 294294c71ba4..d880296245c5 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -170,7 +170,7 @@ static __always_inline void clear_pending_set_locked(struct qspinlock *lock) * @tail : The new queue tail code word * Return: The previous queue tail code word * - * xchg(lock, tail) + * xchg(lock, tail), which heads an address dependency * * p,*,* -> n,*,* ; prev = xchg(lock, node) */ @@ -379,6 +379,14 @@ queue: tail = encode_tail(smp_processor_id(), idx); node += idx; + + /* + * Ensure that we increment the head node->count before initialising + * the actual node. If the compiler is kind enough to reorder these + * stores, then an IRQ could overwrite our assignments. + */ + barrier(); + node->locked = 0; node->next = NULL; pv_init_node(node); @@ -408,16 +416,15 @@ queue: */ if (old & _Q_TAIL_MASK) { prev = decode_tail(old); + /* - * The above xchg_tail() is also a load of @lock which generates, - * through decode_tail(), a pointer. - * - * The address dependency matches the RELEASE of xchg_tail() - * such that the access to @prev must happen after. + * We must ensure that the stores to @node are observed before + * the write to prev->next. The address dependency from + * xchg_tail is not sufficient to ensure this because the read + * component of xchg_tail is unordered with respect to the + * initialisation of @node. */ - smp_read_barrier_depends(); - - WRITE_ONCE(prev->next, node); + smp_store_release(&prev->next, node); pv_wait_node(node, prev); arch_mcs_spin_lock_contended(&node->locked); |