[PATCH rcu 0/7] Documentation updates for v6.6

[PATCH rcu 0/7] Documentation updates for v6.6

[Paul E. McKenney]

Hello!

This series contains documentation updates:

1.	documentation/rcu: Fix typo, courtesy of Tycho Andersen.

2.	docs/RCU: Add the missing rcu_read_unlock(), courtesy of Alan
	Huang.

3.	Docs/RCU/rculist_nulls: Fix trivial coding style, courtesy of
	SeongJae Park.

4.	Docs/RCU/rculist_nulls: Assign 'obj' before use from the examples,
	courtesy of SeongJae Park.

5.	Docs/RCU/rculist_nulls: Specify type of the object in examples,
	courtesy of SeongJae Park.

6.	Docs/RCU/rculist_nulls: Fix hlist_[nulls]_head field names of
	'obj', courtesy of SeongJae Park.

7.	Docs/RCU/rculist_nulls: Fix text about atomic_set_release(),
	courtesy of SeongJae Park.

						Thanx, Paul

------------------------------------------------------------------------

 Documentation/RCU/rculist_nulls.rst   |   38 +++++++++++++++++++++++-----------
 b/Documentation/RCU/lockdep-splat.rst |    2 -
 b/Documentation/RCU/rculist_nulls.rst |    4 ++-
 3 files changed, 30 insertions(+), 14 deletions(-)

[PATCH rcu 1/7] documentation/rcu: Fix typo

[Paul E. McKenney]

From: Tycho Andersen <tandersen@netflix.com>

s/slat/splat/

Signed-off-by: Tycho Andersen <tandersen@netflix.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 Documentation/RCU/lockdep-splat.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/RCU/lockdep-splat.rst b/Documentation/RCU/lockdep-splat.rst
index 2a5c79db57dc..bcbc4b3c88d7 100644
--- a/Documentation/RCU/lockdep-splat.rst
+++ b/Documentation/RCU/lockdep-splat.rst
@@ -10,7 +10,7 @@ misuses of the RCU API, most notably using one of the rcu_dereference()
 family to access an RCU-protected pointer without the proper protection.
 When such misuse is detected, an lockdep-RCU splat is emitted.
 
-The usual cause of a lockdep-RCU slat is someone accessing an
+The usual cause of a lockdep-RCU splat is someone accessing an
 RCU-protected data structure without either (1) being in the right kind of
 RCU read-side critical section or (2) holding the right update-side lock.
 This problem can therefore be serious: it might result in random memory
-- 
2.40.1

[PATCH rcu 2/7] docs/RCU: Add the missing rcu_read_unlock()

[Paul E. McKenney]

From: Alan Huang <mmpgouride@gmail.com>

We should exit the RCU read-side critical section before re-entering.

Signed-off-by: Alan Huang <mmpgouride@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 Documentation/RCU/rculist_nulls.rst | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst
index 9a734bf54b76..0612a6387d8e 100644
--- a/Documentation/RCU/rculist_nulls.rst
+++ b/Documentation/RCU/rculist_nulls.rst
@@ -29,8 +29,10 @@ algorithms:
   rcu_read_lock()
   obj = lockless_lookup(key);
   if (obj) {
-    if (!try_get_ref(obj)) // might fail for free objects
+    if (!try_get_ref(obj)) { // might fail for free objects
+      rcu_read_unlock();
       goto begin;
+    }
     /*
     * Because a writer could delete object, and a writer could
     * reuse these object before the RCU grace period, we
-- 
2.40.1

[PATCH rcu 3/7] Docs/RCU/rculist_nulls: Fix trivial coding style

[Paul E. McKenney]

From: SeongJae Park <sj@kernel.org>

Lookup example of non-hlist_nulls management is missing a semicolon, and
having inconsistent indentation (one line is using single space
indentation while others are using two spaces indentation).  Fix the
trivial issues.

Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 Documentation/RCU/rculist_nulls.rst | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst
index 0612a6387d8e..25b739885cfa 100644
--- a/Documentation/RCU/rculist_nulls.rst
+++ b/Documentation/RCU/rculist_nulls.rst
@@ -26,7 +26,7 @@ algorithms:
 ::
 
   begin:
-  rcu_read_lock()
+  rcu_read_lock();
   obj = lockless_lookup(key);
   if (obj) {
     if (!try_get_ref(obj)) { // might fail for free objects
@@ -70,8 +70,8 @@ And note the traditional hlist_for_each_entry_rcu() misses this smp_rmb()::
        pos && ({ prefetch(pos->next); 1; }) &&
        ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; });
        pos = rcu_dereference(pos->next))
-   if (obj->key == key)
-     return obj;
+    if (obj->key == key)
+      return obj;
   return NULL;
 
 Quoting Corey Minyard::
-- 
2.40.1

[PATCH rcu 4/7] Docs/RCU/rculist_nulls: Assign 'obj' before use from the examples

[Paul E. McKenney]

From: SeongJae Park <sj@kernel.org>

Lookup example code snippets in rculist_nulls.rst are using 'obj'
without assignment.  Fix the code to assign it properly.

Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 Documentation/RCU/rculist_nulls.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst
index 25b739885cfa..4d6f077552ed 100644
--- a/Documentation/RCU/rculist_nulls.rst
+++ b/Documentation/RCU/rculist_nulls.rst
@@ -56,7 +56,7 @@ 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; }) &&
-         ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; });
+         ({ obj = hlist_entry(pos, typeof(*obj), member); 1; });
          pos = rcu_dereference(next))
       if (obj->key == key)
         return obj;
@@ -68,7 +68,7 @@ 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; }) &&
-       ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; });
+       ({ obj = hlist_entry(pos, typeof(*obj), member); 1; });
        pos = rcu_dereference(pos->next))
     if (obj->key == key)
       return obj;
-- 
2.40.1

[PATCH rcu 5/7] Docs/RCU/rculist_nulls: Specify type of the object in examples

[Paul E. McKenney]

From: SeongJae Park <sj@kernel.org>

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>
Signed-off-by: Paul E. McKenney <paulmck@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 4d6f077552ed..479cedfec446 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
 -------------------
@@ -144,6 +153,9 @@ 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
 -------------------
-- 
2.40.1

[PATCH rcu 6/7] Docs/RCU/rculist_nulls: Fix hlist_[nulls]_head field names of 'obj'

[Paul E. McKenney]

From: SeongJae Park <sj@kernel.org>

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>
Signed-off-by: Paul E. McKenney <paulmck@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 479cedfec446..1fb086066377 100644
--- a/Documentation/RCU/rculist_nulls.rst
+++ b/Documentation/RCU/rculist_nulls.rst
@@ -65,7 +65,7 @@ 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;
@@ -77,7 +77,7 @@ 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;
@@ -97,7 +97,7 @@ 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
@@ -165,7 +165,7 @@ 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();
-- 
2.40.1

[PATCH rcu 7/7] Docs/RCU/rculist_nulls: Fix text about atomic_set_release()

[Paul E. McKenney]

From: SeongJae Park <sj@kernel.org>

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>
Signed-off-by: Paul E. McKenney <paulmck@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 1fb086066377..21e40fcc08de 100644
--- a/Documentation/RCU/rculist_nulls.rst
+++ b/Documentation/RCU/rculist_nulls.rst
@@ -140,8 +140,7 @@ 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
@@ -196,6 +195,9 @@ 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().
+
 ::
 
   /*
-- 
2.40.1