Re: [(RT RFC) PATCH v2 3/9] rearrange rt_spin_lock sleep

[Gregory Haskins]

>>> On Mon, Feb 25, 2008 at  4:54 PM, in message
<20080225215454.GF2659@xxxxxxxxxx>, Pavel Machek <pavel@xxxxxx> wrote: 
> Hi!
> 
>> @@ -720,7 +728,8 @@ rt_spin_lock_slowlock(struct rt_mutex *lock)
>>  	 * saved_state accordingly. If we did not get a real wakeup
>>  	 * then we return with the saved state.
>>  	 */
>> -	saved_state = xchg(&current->state, TASK_UNINTERRUPTIBLE);
>> +	saved_state = current->state;
>> +	smp_mb();
>>  
>>  	for (;;) {
>>  		unsigned long saved_flags;
> 
> Please document what the barrier is good for.

Yeah, I think you are right that this isn't needed.  I think that is a relic from back when I was debugging some other problems.  Let me wrap my head around the implications of removing it, and either remove it or document appropriately.

> 
> Plus, you are replacing atomic operation with nonatomic; is that ok?

Yeah, I think so.  We are substituting a write with a read, and word reads are always atomic anyway IIUC (or is that only true on certain architectures)?  Note that we are moving the atomic-write to be done later in the update_current() calls.

-Greg



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