[PATCH] Doc/RCU: fix pseudocode in rcuref.txt

[PATCH] Doc/RCU: fix pseudocode in rcuref.txt

[Lai Jiangshan]

atomic_inc_not_zero(v) return 0 if *v = 0.
use spin_lock instead of write_lock for update lock.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt
index 451de2a..4202ad0 100644
--- a/Documentation/RCU/rcuref.txt
+++ b/Documentation/RCU/rcuref.txt
@@ -29,9 +29,9 @@ release_referenced()			delete()
 					}
 
 If this list/array is made lock free using RCU as in changing the
-write_lock() in add() and delete() to spin_lock and changing read_lock
-in search_and_reference to rcu_read_lock(), the atomic_get in
-search_and_reference could potentially hold reference to an element which
+write_lock() in add() and delete() to spin_lock() and changing read_lock()
+in search_and_reference() to rcu_read_lock(), the atomic_inc() in
+search_and_reference() could potentially hold reference to an element which
 has already been deleted from the list/array.  Use atomic_inc_not_zero()
 in this scenario as follows:
 
@@ -40,20 +40,20 @@ add()					search_and_reference()
 {					{
     alloc_object			    rcu_read_lock();
     ...					    search_for_element
-    atomic_set(&el->rc, 1);		    if (atomic_inc_not_zero(&el->rc)) {
-    write_lock(&list_lock);		        rcu_read_unlock();
+    atomic_set(&el->rc, 1);		    if (!atomic_inc_not_zero(&el->rc)) {
+    spin_lock(&list_lock);		        rcu_read_unlock();
 					        return FAIL;
     add_element				    }
     ...					    ...
-    write_unlock(&list_lock);		    rcu_read_unlock();
+    spin_unlock(&list_lock);		    rcu_read_unlock();
 }					}
 3.					4.
 release_referenced()			delete()
 {					{
-    ...					    write_lock(&list_lock);
+    ...					    spin_lock(&list_lock);
     if (atomic_dec_and_test(&el->rc))       ...
         call_rcu(&el->head, el_free);       delete_element
-    ...                                     write_unlock(&list_lock);
+    ...                                     spin_unlock(&list_lock);
 } 					    ...
 					    if (atomic_dec_and_test(&el->rc))
 					        call_rcu(&el->head, el_free);

Re: [PATCH] Doc/RCU: fix pseudocode in rcuref.txt

[Ingo Molnar]

* Lai Jiangshan <laijs@cn.fujitsu.com> wrote:

> atomic_inc_not_zero(v) return 0 if *v = 0.
> use spin_lock instead of write_lock for update lock.
> 
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>

i've applied it to tip/core/rcu (unless Paul has objections) - thanks!

	Ingo

Re: [PATCH] Doc/RCU: fix pseudocode in rcuref.txt

[Paul E. McKenney]

On Wed, Sep 10, 2008 at 11:01:07AM +0800, Lai Jiangshan wrote:
> 
> atomic_inc_not_zero(v) return 0 if *v = 0.
> use spin_lock instead of write_lock for update lock.

Good catch, Jiangshan, thank you!

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt
> index 451de2a..4202ad0 100644
> --- a/Documentation/RCU/rcuref.txt
> +++ b/Documentation/RCU/rcuref.txt
> @@ -29,9 +29,9 @@ release_referenced()			delete()
>  					}
> 
>  If this list/array is made lock free using RCU as in changing the
> -write_lock() in add() and delete() to spin_lock and changing read_lock
> -in search_and_reference to rcu_read_lock(), the atomic_get in
> -search_and_reference could potentially hold reference to an element which
> +write_lock() in add() and delete() to spin_lock() and changing read_lock()
> +in search_and_reference() to rcu_read_lock(), the atomic_inc() in
> +search_and_reference() could potentially hold reference to an element which
>  has already been deleted from the list/array.  Use atomic_inc_not_zero()
>  in this scenario as follows:
> 
> @@ -40,20 +40,20 @@ add()					search_and_reference()
>  {					{
>      alloc_object			    rcu_read_lock();
>      ...					    search_for_element
> -    atomic_set(&el->rc, 1);		    if (atomic_inc_not_zero(&el->rc)) {
> -    write_lock(&list_lock);		        rcu_read_unlock();
> +    atomic_set(&el->rc, 1);		    if (!atomic_inc_not_zero(&el->rc)) {
> +    spin_lock(&list_lock);		        rcu_read_unlock();
>  					        return FAIL;
>      add_element				    }
>      ...					    ...
> -    write_unlock(&list_lock);		    rcu_read_unlock();
> +    spin_unlock(&list_lock);		    rcu_read_unlock();
>  }					}
>  3.					4.
>  release_referenced()			delete()
>  {					{
> -    ...					    write_lock(&list_lock);
> +    ...					    spin_lock(&list_lock);
>      if (atomic_dec_and_test(&el->rc))       ...
>          call_rcu(&el->head, el_free);       delete_element
> -    ...                                     write_unlock(&list_lock);
> +    ...                                     spin_unlock(&list_lock);
>  } 					    ...
>  					    if (atomic_dec_and_test(&el->rc))
>  					        call_rcu(&el->head, el_free);
> 
> 

Re: [PATCH] Doc/RCU: fix pseudocode in rcuref.txt

[Paul E. McKenney]

On Wed, Sep 10, 2008 at 08:37:45AM +0200, Ingo Molnar wrote:
> 
> * Lai Jiangshan <laijs@cn.fujitsu.com> wrote:
> 
> > atomic_inc_not_zero(v) return 0 if *v = 0.
> > use spin_lock instead of write_lock for update lock.
> > 
> > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> 
> i've applied it to tip/core/rcu (unless Paul has objections) - thanks!

No objections here!!!

							Thanx, Paul