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authorDavid S. Miller <davem@davemloft.net>2008-10-11 12:39:35 -0700
committerDavid S. Miller <davem@davemloft.net>2008-10-11 12:39:35 -0700
commit56c5d900dbb8e042bfad035d18433476931d8f93 (patch)
tree00b793965beeef10db03e0ff021d2d965c410759 /Documentation/RCU/rcuref.txt
parent4dd95b63ae25c5cad6986829b5e8788e9faa0330 (diff)
parentead9d23d803ea3a73766c3cb27bf7563ac8d7266 (diff)
downloadop-kernel-dev-56c5d900dbb8e042bfad035d18433476931d8f93.zip
op-kernel-dev-56c5d900dbb8e042bfad035d18433476931d8f93.tar.gz
Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/torvalds/linux-2.6
Conflicts: sound/core/memalloc.c
Diffstat (limited to 'Documentation/RCU/rcuref.txt')
-rw-r--r--Documentation/RCU/rcuref.txt16
1 files changed, 8 insertions, 8 deletions
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);
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