Messages in this thread | | | Date | Sun, 15 Feb 2015 17:17:33 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH V5] x86 spinlock: Fix memory corruption on completing completions |
| |
Well, I regret I mentioned the lack of barrier after enter_slowpath ;)
On 02/15, Raghavendra K T wrote: > > @@ -46,7 +46,8 @@ static __always_inline bool static_key_false(struct static_key *key); > > static inline void __ticket_enter_slowpath(arch_spinlock_t *lock) > { > - set_bit(0, (volatile unsigned long *)&lock->tickets.tail); > + set_bit(0, (volatile unsigned long *)&lock->tickets.head); > + barrier(); > }
Because this barrier() looks really confusing.
Firsty, it is equally unneeded on x86. At the same time, it can not help. We need a memory barrier() between set_bit(SLOWPATH) and READ_ONCE(head) to avoid the race with spin_unlock().
So I think you should replace it with smp_mb__after_atomic() or remove it.
Other than that I believe this version is correct. So I won't insist, this is cosmetic after all.
Oleg.
| |