Re: [PATCH V3] x86 spinlock: Fix memory corruption on completing completions
From: Oleg Nesterov <oleg@redhat.com>
Date: 2015-02-12 13:53:24
Also in:
kvm, lkml
On 02/12, Raghavendra K T wrote:
quoted hunk ↗ jump to hunk
@@ -191,8 +189,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t *lock) * We need to check "unlocked" in a loop, tmp.head == head * can be false positive because of overflow. */ - if (tmp.head == (tmp.tail & ~TICKET_SLOWPATH_FLAG) || - tmp.head != head) + if (__tickets_equal(tmp.head, tmp.tail) || tmp.head != head) break;
Ah, it seems that "tmp.head != head" should be turned into !__tickets_equal(), no? Suppose that TICKET_SLOWPATH_FLAG is set after the first ACCESS_ONCE(head), then tmp.head != head will be true before the first unlock we are waiting for. And perhaps you can turn these ACCESS_ONCE into READ_ONCE as well. Oleg.