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

[Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>]

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.