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

[Raghavendra K T]

On 02/12/2015 07:32 PM, Oleg Nesterov wrote:
> 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)".

right, the above if ( ) is unnecesary, though we would have same code
at the end, getting rid of that makes code more clean.

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