Re: [Xen-devel] [PATCHv3 3/4] xen: use ticket locks for spin locks

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.04.15 at 14:03, <tim@xxxxxxx> wrote:
> At 11:11 +0100 on 21 Apr (1429614687), David Vrabel wrote:
>>  void _spin_unlock(spinlock_t *lock)
>>  {
>> +    smp_mb();
>>      preempt_enable();
>>      LOCK_PROFILE_REL;
>> -    _raw_spin_unlock(&lock->raw);
>> +    lock->tickets.head++;
> 
> This needs to be done with an explicit atomic (though not locked)
> write; otherwise the compiler might use some unsuitable operation that
> clobbers .tail as well.

How do you imagine that to happen? An increment of one
structure member surely won't modify any others.

Jan



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel