[RFC,02/21] list: Remove hlist_nulls_unhashed_lockless()
diff mbox series

Message ID 20200324153643.15527-3-will@kernel.org
State New
Headers show
Series
  • Improve list integrity checking
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Commit Message

Will Deacon March 24, 2020, 3:36 p.m. UTC
Commit 02b99b38f3d9 ("rcu: Add a hlist_nulls_unhashed_lockless() function")
introduced the (as yet unused) hlist_nulls_unhashed_lockless() function
to avoid KCSAN reports when an RCU reader checks the 'hashed' status
of an 'hlist_nulls' concurrently undergoing modification.

Remove the unused function and add a READ_ONCE() to hlist_nulls_unhashed(),
just like we do already for hlist_nulls_empty().

Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/list_nulls.h | 14 --------------
 1 file changed, 14 deletions(-)

Comments

Greg KH March 24, 2020, 4:27 p.m. UTC | #1
On Tue, Mar 24, 2020 at 03:36:24PM +0000, Will Deacon wrote:
> Commit 02b99b38f3d9 ("rcu: Add a hlist_nulls_unhashed_lockless() function")
> introduced the (as yet unused) hlist_nulls_unhashed_lockless() function
> to avoid KCSAN reports when an RCU reader checks the 'hashed' status
> of an 'hlist_nulls' concurrently undergoing modification.
> 
> Remove the unused function and add a READ_ONCE() to hlist_nulls_unhashed(),
> just like we do already for hlist_nulls_empty().
> 
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  include/linux/list_nulls.h | 14 --------------
>  1 file changed, 14 deletions(-)

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Paul E. McKenney March 30, 2020, 11:07 p.m. UTC | #2
On Tue, Mar 24, 2020 at 03:36:24PM +0000, Will Deacon wrote:
> Commit 02b99b38f3d9 ("rcu: Add a hlist_nulls_unhashed_lockless() function")
> introduced the (as yet unused) hlist_nulls_unhashed_lockless() function
> to avoid KCSAN reports when an RCU reader checks the 'hashed' status
> of an 'hlist_nulls' concurrently undergoing modification.
> 
> Remove the unused function and add a READ_ONCE() to hlist_nulls_unhashed(),
> just like we do already for hlist_nulls_empty().
> 
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Will Deacon <will@kernel.org>

Well, I guess that the added docbook comment might be seen as worthwhile.

Acked-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  include/linux/list_nulls.h | 14 --------------
>  1 file changed, 14 deletions(-)
> 
> diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
> index fa6e8471bd22..3a9ff01e9a11 100644
> --- a/include/linux/list_nulls.h
> +++ b/include/linux/list_nulls.h
> @@ -65,20 +65,6 @@ static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
>   * but hlist_nulls_del() does not.
>   */
>  static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
> -{
> -	return !h->pprev;
> -}
> -
> -/**
> - * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
> - * @h: Node to be checked
> - *
> - * Not that not all removal functions will leave a node in unhashed state.
> - * For example, hlist_del_init_rcu() leaves the node in unhashed state,
> - * but hlist_nulls_del() does not.  Unlike hlist_nulls_unhashed(), this
> - * function may be used locklessly.
> - */
> -static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
>  {
>  	return !READ_ONCE(h->pprev);
>  }
> -- 
> 2.20.1
>

Patch
diff mbox series

diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
index fa6e8471bd22..3a9ff01e9a11 100644
--- a/include/linux/list_nulls.h
+++ b/include/linux/list_nulls.h
@@ -65,20 +65,6 @@  static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
  * but hlist_nulls_del() does not.
  */
 static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
-{
-	return !h->pprev;
-}
-
-/**
- * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
- * @h: Node to be checked
- *
- * Not that not all removal functions will leave a node in unhashed state.
- * For example, hlist_del_init_rcu() leaves the node in unhashed state,
- * but hlist_nulls_del() does not.  Unlike hlist_nulls_unhashed(), this
- * function may be used locklessly.
- */
-static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
 {
 	return !READ_ONCE(h->pprev);
 }