Re: [Xen-devel] [PATCH V3] x86 spinlock: Fix memory corruption on completing completions

[Oleg Nesterov <oleg@xxxxxxxxxx>]

Damn, sorry for noise, forgot to mention...

On 02/12, Raghavendra K T wrote:
>
> +static inline void __ticket_check_and_clear_slowpath(arch_spinlock_t *lock,
> +                                                     __ticket_t head)
> +{
> +     if (head & TICKET_SLOWPATH_FLAG) {
> +             arch_spinlock_t old, new;
> +
> +             old.tickets.head = head;
> +             new.tickets.head = head & ~TICKET_SLOWPATH_FLAG;
> +             old.tickets.tail = new.tickets.head + TICKET_LOCK_INC;
> +             new.tickets.tail = old.tickets.tail;
> +
> +             /* try to clear slowpath flag when there are no contenders */
> +             cmpxchg(&lock->head_tail, old.head_tail, new.head_tail);
> +     }
> +}

...

> +clear_slowpath:
> +     if (TICKET_SLOWPATH_FLAG)
> +             __ticket_check_and_clear_slowpath(lock, inc.head);

I think you can remove this "if (TICKET_SLOWPATH_FLAG)" check. If it is
defined as zero, gcc should optimize out the code under "if (head & 0)".

But this is purely cosmetic and subjective, feel free to ignore.

Oleg.


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