Messages in this thread | | | Date | Thu, 12 Feb 2015 14:50:56 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH V3] x86 spinlock: Fix memory corruption on completing completions |
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On 02/12, Raghavendra K T wrote: > > @@ -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.
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