Re: [PATCH V4] x86 spinlock: Fix memory corruption on completing completions

[Oleg Nesterov]

On 02/13, Oleg Nesterov wrote:
>
> On 02/13, Raghavendra K T wrote:
> >
> > @@ -772,7 +773,8 @@ __visible void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
> >  	 * check again make sure it didn't become free while
> >  	 * we weren't looking.
> >  	 */
> > -	if (ACCESS_ONCE(lock->tickets.head) == want) {
> > +	head = READ_ONCE(lock->tickets.head);
> > +	if (__tickets_equal(head, want)) {
> >  		add_stats(TAKEN_SLOW_PICKUP, 1);
> >  		goto out;
>
> This is off-topic, but with or without this change perhaps it makes sense
> to add smp_mb__after_atomic(). It is nop on x86, just to make this code
> more understandable for those (for me ;) who can never remember even the
> x86 rules.

Not that I think you should do this in v5, so please ignore.

Oleg.

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