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

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);
+       }


+               __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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