[PATCH v4 0/3] Docs/RCU/rculist_nulls: Minor fixup

[PATCH v4 0/3] Docs/RCU/rculist_nulls: Minor fixup

[SeongJae Park]

Changes from v3
(https://lore.kernel.org/rcu/20230615181004.86850-1-sj@kernel.org/)
- Fix Paul's name on 'Suggested-by:' tag
- Use 'atomic_t' for refcnt field of 'struct object'

Changes from v2
(https://lore.kernel.org/rcu/20230613182434.88317-1-sj@kernel.org/)
- Drop first two patches that merged to Paul's tree
- Add definition of 'obj' (Paul E. McKenney)
- Fix more wrong hlist_[nulls]_head field name mentions

Changes from v1
(https://lore.kernel.org/rcu/20230518224008.2468-1-sj@kernel.org/)
- Add Reviewed-by tags from Joel Fernandes for first three patches
- Fix the text for wrong extra _release()

---

Fix minor problems in example code snippets and the text of
rculist_nulls.rst file.

SeongJae Park (3):
  Docs/RCU/rculist_nulls: Specify type of the object in examples
  Docs/RCU/rculist_nulls: Fix hlist_[nulls]_head field names of 'obj'
  Docs/RCU/rculist_nulls: Fix text about atomic_set_release()

 Documentation/RCU/rculist_nulls.rst | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

-- 
2.25.1

[PATCH v4 1/3] Docs/RCU/rculist_nulls: Specify type of the object in examples

[SeongJae Park]

The type of 'obj' in example code of rculist_nulls.rst is implicit.
Provide the specific type of it before the example code.

Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/rcu/43943609-f80c-4b6a-9844-994eef800757@paulmck-laptop/
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 Documentation/RCU/rculist_nulls.rst | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst
index 94a8bfe9f560..a6827cc31791 100644
--- a/Documentation/RCU/rculist_nulls.rst
+++ b/Documentation/RCU/rculist_nulls.rst
@@ -18,7 +18,16 @@ to solve following problem.
 
 Without 'nulls', a typical RCU linked list managing objects which are
 allocated with SLAB_TYPESAFE_BY_RCU kmem_cache can use the following
-algorithms:
+algorithms.  Following examples assume 'obj' is a pointer to such
+objects, which is having below type.
+
+::
+
+  struct object {
+    struct hlist_node obj_node;
+    atomic_t refcnt;
+    unsigned int key;
+  };
 
 1) Lookup algorithm
 -------------------
@@ -142,6 +151,9 @@ the beginning. If the object was moved to the same chain,
 then the reader doesn't care: It might occasionally
 scan the list again without harm.
 
+Note that using hlist_nulls means the type of 'obj_node' field of
+'struct object' becomes 'struct hlist_nulls_node'.
+
 
 1) lookup algorithm
 -------------------
-- 
2.25.1

[PATCH v4 2/3] Docs/RCU/rculist_nulls: Fix hlist_[nulls]_head field names of 'obj'

[SeongJae Park]

The example code snippets on rculist_nulls.rst are assuming 'obj' to
have the 'hlist_head' or 'hlist_nulls_head' field named 'obj_node', but
a sentence and some code snippets are wrongly calling
'obj->obj_node.next' as 'obj->obj_next', or 'obj->obj_node' as 'member'.
Fix it.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 Documentation/RCU/rculist_nulls.rst | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst
index a6827cc31791..4afa11f2c906 100644
--- a/Documentation/RCU/rculist_nulls.rst
+++ b/Documentation/RCU/rculist_nulls.rst
@@ -63,7 +63,7 @@ but a version with an additional memory barrier (smp_rmb())
     struct hlist_node *node, *next;
     for (pos = rcu_dereference((head)->first);
          pos && ({ next = pos->next; smp_rmb(); prefetch(next); 1; }) &&
-         ({ obj = hlist_entry(pos, typeof(*obj), member); 1; });
+         ({ obj = hlist_entry(pos, typeof(*obj), obj_node); 1; });
          pos = rcu_dereference(next))
       if (obj->key == key)
         return obj;
@@ -75,7 +75,7 @@ And note the traditional hlist_for_each_entry_rcu() misses this smp_rmb()::
   struct hlist_node *node;
   for (pos = rcu_dereference((head)->first);
        pos && ({ prefetch(pos->next); 1; }) &&
-       ({ obj = hlist_entry(pos, typeof(*obj), member); 1; });
+       ({ obj = hlist_entry(pos, typeof(*obj), obj_node); 1; });
        pos = rcu_dereference(pos->next))
     if (obj->key == key)
       return obj;
@@ -95,7 +95,7 @@ Quoting Corey Minyard::
 2) Insertion algorithm
 ----------------------
 
-We need to make sure a reader cannot read the new 'obj->obj_next' value
+We need to make sure a reader cannot read the new 'obj->obj_node.next' value
 and previous value of 'obj->key'. Otherwise, an item could be deleted
 from a chain, and inserted into another chain. If new chain was empty
 before the move, 'next' pointer is NULL, and lockless reader can not
@@ -163,7 +163,7 @@ Note that using hlist_nulls means the type of 'obj_node' field of
   head = &table[slot];
   begin:
   rcu_read_lock();
-  hlist_nulls_for_each_entry_rcu(obj, node, head, member) {
+  hlist_nulls_for_each_entry_rcu(obj, node, head, obj_node) {
     if (obj->key == key) {
       if (!try_get_ref(obj)) { // might fail for free objects
 	rcu_read_unlock();
-- 
2.25.1

[PATCH v4 3/3] Docs/RCU/rculist_nulls: Fix text about atomic_set_release()

[SeongJae Park]

The document says we can avoid extra _release() in insert function when
hlist_nulls is used, but that's not true[1].  Drop it.

[1] https://lore.kernel.org/rcu/46440869-644a-4982-b790-b71b43976c66@paulmck-laptop/

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 Documentation/RCU/rculist_nulls.rst | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst
index 4afa11f2c906..660cc3f0f1e5 100644
--- a/Documentation/RCU/rculist_nulls.rst
+++ b/Documentation/RCU/rculist_nulls.rst
@@ -138,8 +138,7 @@ very very fast (before the end of RCU grace period)
 Avoiding extra smp_rmb()
 ========================
 
-With hlist_nulls we can avoid extra smp_rmb() in lockless_lookup()
-and extra _release() in insert function.
+With hlist_nulls we can avoid extra smp_rmb() in lockless_lookup().
 
 For example, if we choose to store the slot number as the 'nulls'
 end-of-list marker for each slot of the hash table, we can detect
@@ -194,6 +193,9 @@ Note that using hlist_nulls means the type of 'obj_node' field of
 2) Insert algorithm
 -------------------
 
+Same to the above one, but uses hlist_nulls_add_head_rcu() instead of
+hlist_add_head_rcu().
+
 ::
 
   /*
-- 
2.25.1

Re: [PATCH v4 0/3] Docs/RCU/rculist_nulls: Minor fixup

[Paul E. McKenney]

On Fri, Jun 16, 2023 at 11:36:23PM +0000, SeongJae Park wrote:
> Changes from v3
> (https://lore.kernel.org/rcu/20230615181004.86850-1-sj@kernel.org/)
> - Fix Paul's name on 'Suggested-by:' tag
> - Use 'atomic_t' for refcnt field of 'struct object'
> 
> Changes from v2
> (https://lore.kernel.org/rcu/20230613182434.88317-1-sj@kernel.org/)
> - Drop first two patches that merged to Paul's tree
> - Add definition of 'obj' (Paul E. McKenney)
> - Fix more wrong hlist_[nulls]_head field name mentions
> 
> Changes from v1
> (https://lore.kernel.org/rcu/20230518224008.2468-1-sj@kernel.org/)
> - Add Reviewed-by tags from Joel Fernandes for first three patches
> - Fix the text for wrong extra _release()
> 
> ---
> 
> Fix minor problems in example code snippets and the text of
> rculist_nulls.rst file.

I am replacing the earlier versions with this version, thank you!!!

						Thanx, Paul

> SeongJae Park (3):
>   Docs/RCU/rculist_nulls: Specify type of the object in examples
>   Docs/RCU/rculist_nulls: Fix hlist_[nulls]_head field names of 'obj'
>   Docs/RCU/rculist_nulls: Fix text about atomic_set_release()
> 
>  Documentation/RCU/rculist_nulls.rst | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)
> 
> -- 
> 2.25.1
>