[PATCH] fix gettimeofday vs. update_gtod race

[Benjamin Herrenschmidt]

On Wed, 2006-08-16 at 19:18 -0500, Nathan Lynch wrote:

> No?  I didn't find anything about mftb having synchronizing
> behavior.  How should we ensure that temp_varp is assigned before
> reading the timebase?

I sync an isync would be enough.

> Surely at least a compiler barrier is needed?

Yeah.

> > and the race not completely closed imho... 
> 
> How so?  I could've missed something, but I've hammered the patch
> pretty hard, fwiw.

Nah you are right, but you may be using a too big hammer

> > I need to think about it a bit more closely but what about instead
> > just check if tb_ticks goes negative, and if yes, just do get_tb()
> > again ?  That might be faster than having a sync in there and should
> > still be correct.
> 
> I did try something like that but found that a loop (i.e. multiple
> get_tb's to "catch up") was necessary.

Hrm... even with an isync ?

Ben.