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doc/RCU: fix pseudocode in rcuref.txt

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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>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Lai Jiangshan 2008-09-10 11:01:07 +08:00 committed by Ingo Molnar
parent 429b022af4
commit e8aed68614
1 changed files with 8 additions and 8 deletions
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16
Documentation/RCU/rcuref.txt
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@ -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);