Re: rcu_read_lock lost its compiler barrier

[Herbert Xu]

On Thu, Jun 06, 2019 at 03:58:17AM -0700, Paul E. McKenney wrote:
>
> I cannot immediately think of a way that the compiler could get this
> wrong even in theory, but similar code sequences can be messed up.
> The reason for this is that in theory, the compiler could use the
> stored-to location as temporary storage, like this:
> 
> 	a = whatever;	// Compiler uses "a" as a temporary
> 	do_something();
> 	whatever = a;
> 	a = 1;		// Intended store

Well if the compiler is going to do this then surely it would
continue to do this even if you used WRITE_ONCE.  Remember a is
not volatile, only the access of a through WRITE_ONCE is volatile.

Cheers,
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
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