On Mon, May 24, 2021 at 6:33 PM Boqun Feng [off-list ref] wrote:

On Mon, May 24, 2021 at 12:24:00PM +0800, Xiongwei Song wrote:

quoted

On Fri, May 21, 2021 at 11:17 PM Waiman Long [off-list ref] wrote:

quoted

On 5/21/21 2:29 AM, Xiongwei Song wrote:

quoted

From: Xiongwei Song <redacted>

The block condition matrix is using 'E' as the writer noation here, so it
would be better to use 'E' as the reminder rather than 'W'.

Signed-off-by: Xiongwei Song <redacted>
---
  Documentation/locking/lockdep-design.rst | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/locking/lockdep-design.rst b/Documentation/locking/lockdep-design.rst
index 9f3cfca..c3b923a 100644
--- a/Documentation/locking/lockdep-design.rst
+++ b/Documentation/locking/lockdep-design.rst

@@ -462,7 +462,7 @@ Block condition matrix, Y means the row blocks the column, and N means otherwise
      | R | Y | Y | N |
      +---+---+---+---+

-     (W: writers, r: non-recursive readers, R: recursive readers)
+     (E: writers, r: non-recursive readers, R: recursive readers)


  acquired recursively. Unlike non-recursive read locks, recursive read locks

I would say it should be the other way around. Both W and E refer to the
same type of lockers. W emphasizes writer aspect of it and E for
exclusive. I think we should change the block condition matrix to use W
instead of E.

The doc uses 'E'  to describe dependency egdes too. Should we change them
to 'W'? Personally,  both 'W' and 'E' are fine.

I also think Waiman's suggestion is solid, there are two ways to
classify locks:

1.      W (Writers), R (Recursive Readers), r (Non-recursive Readers)

2.      E (Exclusive locks), S (Shared locks), R (Recursive Readers),
        N (Non-recursive locks)

And the relations between them are as follow:

        E = W
        R = R
        N = W \/ r
        S = R \/ r

, where "\/" is the set union.

The story is that I used the way #1 at first, and later on realized way
#2 is better for BFS implementation, also for reasoning, so here came
this leftover..

Thanks for the explanation.

If you are interested, go ahead sending a patch fixing this, otherwise,
I will fix this.

Ok.  Let me fix.

Thanks,
Xiongwei

Regards,
Boqun

quoted

Thanks,
Xiongwei

quoted

Cheers,
Longman