[PATCH 0/2] mm/slab: trivial fixup for SLAB_TYPESAFE_BY_RCU example code snippet

[PATCH 0/2] mm/slab: trivial fixup for SLAB_TYPESAFE_BY_RCU example code snippet

[SeongJae Park]

This patchset is for trivial fixup for SLAB_TYPESAFE_BY_RCU example code
snippet, namely adding missed semicolon and breaking RCU read-side
critical section into smaller ones.

SeongJae Park (2):
  mm/slab: add a missing semicolon on SLAB_TYPESAFE_BY_RCU example code
  mm/slab: break up RCU readers on SLAB_TYPESAFE_BY_RCU example code

 include/linux/slab.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

-- 
2.25.1

[PATCH 1/2] mm/slab: add a missing semicolon on SLAB_TYPESAFE_BY_RCU example code

[SeongJae Park]

An example code snippet for SLAB_TYPESAFE_BY_RCU is missing a semicolon.
Add it.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/slab.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index f8b1d63c63a3..b18e56c6f06c 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -53,7 +53,7 @@
  * stays valid, the trick to using this is relying on an independent
  * object validation pass. Something like:
  *
- *  rcu_read_lock()
+ *  rcu_read_lock();
  * again:
  *  obj = lockless_lookup(key);
  *  if (obj) {
-- 
2.25.1

[PATCH 2/2] mm/slab: break up RCU readers on SLAB_TYPESAFE_BY_RCU example code

[SeongJae Park]

The SLAB_TYPESAFE_BY_RCU example code snippet is having not tiny RCU
read-side critical section.  'Documentation/RCU/rculist_nulls.rst' has
similar example code snippet, and commit da82af04352b ("doc: Update and
wordsmith rculist_nulls.rst") has broken it.  Apply the change to
SLAB_TYPESAFE_BY_RCU example code snippet, too.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/slab.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index b18e56c6f06c..a2fd57322c9c 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -53,15 +53,16 @@
  * stays valid, the trick to using this is relying on an independent
  * object validation pass. Something like:
  *
+ * begin:
  *  rcu_read_lock();
- * again:
  *  obj = lockless_lookup(key);
  *  if (obj) {
  *    if (!try_get_ref(obj)) // might fail for free objects
- *      goto again;
+ *      goto begin;
  *
  *    if (obj->key != key) { // not the object we expected
  *      put_ref(obj);
+ *      rcu_read_unlock();
  *      goto again;
  *    }
  *  }
-- 
2.25.1

Re: [PATCH 2/2] mm/slab: break up RCU readers on SLAB_TYPESAFE_BY_RCU example code

[Matthew Wilcox]

On Sat, Apr 15, 2023 at 12:37:53AM +0000, SeongJae Park wrote:
>   *
> + * begin:
>   *  rcu_read_lock();
> - * again:
>   *  obj = lockless_lookup(key);
>   *  if (obj) {
>   *    if (!try_get_ref(obj)) // might fail for free objects
> - *      goto again;
> + *      goto begin;
>   *
>   *    if (obj->key != key) { // not the object we expected
>   *      put_ref(obj);
> + *      rcu_read_unlock();
>   *      goto again;

- *      goto again;
+ *      goto begin;

Re: [PATCH 2/2] mm/slab: break up RCU readers on SLAB_TYPESAFE_BY_RCU example code

[SeongJae Park]

On Sat, 15 Apr 2023 03:51:54 +0100 Matthew Wilcox <willy@infradead.org> wrote:

> On Sat, Apr 15, 2023 at 12:37:53AM +0000, SeongJae Park wrote:
> >   *
> > + * begin:
> >   *  rcu_read_lock();
> > - * again:
> >   *  obj = lockless_lookup(key);
> >   *  if (obj) {
> >   *    if (!try_get_ref(obj)) // might fail for free objects
> > - *      goto again;
> > + *      goto begin;
> >   *
> >   *    if (obj->key != key) { // not the object we expected
> >   *      put_ref(obj);
> > + *      rcu_read_unlock();
> >   *      goto again;
> 
> - *      goto again;
> + *      goto begin;

Oops, thank you for catching, Matthew!


Thanks,
SJ

Re: [PATCH 2/2] mm/slab: break up RCU readers on SLAB_TYPESAFE_BY_RCU example code

[SeongJae Park]

On Sat, 15 Apr 2023 03:04:52 +0000 SeongJae Park <sj@kernel.org> wrote:

> On Sat, 15 Apr 2023 03:51:54 +0100 Matthew Wilcox <willy@infradead.org> wrote:
> 
> > On Sat, Apr 15, 2023 at 12:37:53AM +0000, SeongJae Park wrote:
> > >   *
> > > + * begin:
> > >   *  rcu_read_lock();
> > > - * again:
> > >   *  obj = lockless_lookup(key);
> > >   *  if (obj) {
> > >   *    if (!try_get_ref(obj)) // might fail for free objects
> > > - *      goto again;
> > > + *      goto begin;

I simply followed the commit da82af04352b ("doc: Update and wordsmith
rculist_nulls.rst") for this change, and I think I overlooked this part.  If
I'm not missing something, I think we should call rcu_read_unlock() here too,
just before 'goto begin'.

I will post another patch for rculist_null.rst later.


Thanks,
SJ

> > >   *
> > >   *    if (obj->key != key) { // not the object we expected
> > >   *      put_ref(obj);
> > > + *      rcu_read_unlock();
> > >   *      goto again;
> > 
> > - *      goto again;
> > + *      goto begin;
> 
> Oops, thank you for catching, Matthew!
> 
> 
> Thanks,
> SJ