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authorIngo Molnar <mingo@elte.hu>2008-10-12 12:39:30 +0200
committerIngo Molnar <mingo@elte.hu>2008-10-12 12:39:50 +0200
commit4c7145a1ec1bb789d5f07e47510e8bda546a7c4a (patch)
treee2767b77e5413473a3bba302237f4669a203f183 /Documentation/RCU/rcuref.txt
parent74e91604b2452c15bbe72d77b37cf47ed0310d13 (diff)
parentfd048088306656824958e7783ffcee27e241b361 (diff)
Merge branch 'linus' into x86/spinlocks
Done to prevent this failure of an Octopus merge: Added arch/arm/include/asm/byteorder.h in both, but differently. ERROR: Merge conflict in arch/arm/include/asm/byteorder.h Auto-merging include/asm-x86/spinlock.h ERROR: Merge conflict in include/asm-x86/spinlock.h fatal: merge program failed
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 451de2ad832..4202ad09313 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);