Re: Linux-kernel examples for LKMM recipes

[Alan Stern]

On Wed, 18 Oct 2017, Paul E. McKenney wrote:

> > Well, you could explicitly mention that in the multi-thread case, this
> > means all accesses to the shared variable had better use READ_ONCE() or
> > WRITE_ONCE().
> 
> Like this?
> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> 	d.	If there are multiple CPUs, accesses to shared variables
> 		should use READ_ONCE() and WRITE_ONCE() or stronger
> 		to prevent load/store tearing, load/store fusing, and
> 		invented loads and stores.  There are exceptions to
> 		this rule, for example:
> 
> 		i.	When there is no possibility of a given
> 			shared variable being updated, for example,
> 			while holding the update-side lock, reads
> 			from that variable need not use READ_ONCE().
> 
> 		ii.	When there is no possibility of a given shared
> 			variable being either read or updated, for
> 			example, when running during early boot, reads
> 			from that variable need not use READ_ONCE() and
> 			writes to that variable need not use WRITE_ONCE().

Yeah, except that you mean being read or updated by another thread.

Alan