On Fri, Jan 31, 2020 at 09:52:37PM +0100, SeongJae Park wrote:
> From: SeongJae Park <sjpark@xxxxxxxxx>
>
> Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx>
Good catches, queued, thank you!
But if Jon would rather take this:
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Thanx, Paul
> ---
> Documentation/memory-barriers.txt | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
> index ec3b5865c1be..01ab5e22b670 100644
> --- a/Documentation/memory-barriers.txt
> +++ b/Documentation/memory-barriers.txt
> @@ -185,7 +185,7 @@ As a further example, consider this sequence of events:
> =============== ===============
> { A == 1, B == 2, C == 3, P == &A, Q == &C }
> B = 4; Q = P;
> - P = &B D = *Q;
> + P = &B; D = *Q;
>
> There is an obvious data dependency here, as the value loaded into D depends on
> the address retrieved from P by CPU 2. At the end of the sequence, any of the
> @@ -569,7 +569,7 @@ following sequence of events:
> { A == 1, B == 2, C == 3, P == &A, Q == &C }
> B = 4;
> <write barrier>
> - WRITE_ONCE(P, &B)
> + WRITE_ONCE(P, &B);
> Q = READ_ONCE(P);
> D = *Q;
>
> @@ -1721,7 +1721,7 @@ of optimizations:
> and WRITE_ONCE() are more selective: With READ_ONCE() and
> WRITE_ONCE(), the compiler need only forget the contents of the
> indicated memory locations, while with barrier() the compiler must
> - discard the value of all memory locations that it has currented
> + discard the value of all memory locations that it has currently
> cached in any machine registers. Of course, the compiler must also
> respect the order in which the READ_ONCE()s and WRITE_ONCE()s occur,
> though the CPU of course need not do so.
> @@ -1833,7 +1833,7 @@ Aside: In the case of data dependencies, the compiler would be expected
> to issue the loads in the correct order (eg. `a[b]` would have to load
> the value of b before loading a[b]), however there is no guarantee in
> the C specification that the compiler may not speculate the value of b
> -(eg. is equal to 1) and load a before b (eg. tmp = a[1]; if (b != 1)
> +(eg. is equal to 1) and load a[b] before b (eg. tmp = a[1]; if (b != 1)
> tmp = a[b]; ). There is also the problem of a compiler reloading b after
> having loaded a[b], thus having a newer copy of b than a[b]. A consensus
> has not yet been reached about these problems, however the READ_ONCE()
> --
> 2.17.1
>
