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Commit e8aed686 authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Ingo Molnar
Browse files

doc/RCU: fix pseudocode in rcuref.txt 



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

Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 429b022a

Documentation/RCU/rcuref.txt

+8 −8
Original line number Original line Diff line number Diff line
@@ -29,9 +29,9 @@ release_referenced() delete() 
					}

					}





If this list/array is made lock free using RCU as in changing the

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

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

in search_and_reference() to rcu_read_lock(), the atomic_inc() in

search_and_reference could potentially hold reference to an element which

search_and_reference() could potentially hold reference to an element which

has already been deleted from the list/array.  Use atomic_inc_not_zero()

has already been deleted from the list/array.  Use atomic_inc_not_zero()

in this scenario as follows:

in this scenario as follows:
@@ -40,20 +40,20 @@ add() search_and_reference() 
{					{

{					{

    alloc_object			    rcu_read_lock();

    alloc_object			    rcu_read_lock();

    ...					    search_for_element

    ...					    search_for_element

    atomic_set(&el->rc, 1);		    if (atomic_inc_not_zero(&el->rc)) {

    atomic_set(&el->rc, 1);		    if (!atomic_inc_not_zero(&el->rc)) {

    write_lock(&list_lock);		        rcu_read_unlock();

    spin_lock(&list_lock);		        rcu_read_unlock();

					        return FAIL;

					        return FAIL;

    add_element				    }

    add_element				    }

    ...					    ...

    ...					    ...

    write_unlock(&list_lock);		    rcu_read_unlock();

    spin_unlock(&list_lock);		    rcu_read_unlock();

}					}

}					}

3.					4.

3.					4.

release_referenced()			delete()

release_referenced()			delete()

{					{

{					{

    ...					    write_lock(&list_lock);

    ...					    spin_lock(&list_lock);

    if (atomic_dec_and_test(&el->rc))       ...

    if (atomic_dec_and_test(&el->rc))       ...

        call_rcu(&el->head, el_free);       delete_element

        call_rcu(&el->head, el_free);       delete_element

    ...                                     write_unlock(&list_lock);

    ...                                     spin_unlock(&list_lock);

} 					    ...

} 					    ...

					    if (atomic_dec_and_test(&el->rc))

					    if (atomic_dec_and_test(&el->rc))

					        call_rcu(&el->head, el_free);

					        call_rcu(&el->head, el_free);