[PATCH] lockdep: allow read_lock() recursion of same class

From: Ingo Molnar <mingo@elte.hu>

lockdep so far only allowed read-recursion for the same lock instance.
This is enough in the overwhelming majority of cases, but a hostap case
triggered and reported by Miles Lane relies on same-class
different-instance recursion.  So we relax the restriction on read-lock
recursion.

(This change does not allow rwsem read-recursion, which is still
forbidden.)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 2 insertions, 3 deletions

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index dd0580910a97..f32ca78c198d 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -843,10 +843,9 @@ check_deadlock(struct task_struct *curr, struct held_lock *next,
                         continue;
                 /*
                  * Allow read-after-read recursion of the same
-                 * lock instance (i.e. read_lock(lock)+read_lock(lock)):
+                 * lock class (i.e. read_lock(lock)+read_lock(lock)):
                  */
-                if ((read == 2) && prev->read &&
-                                (prev->instance == next_instance))
+                if ((read == 2) && prev->read)
                         return 2;
                 return print_deadlock_bug(curr, prev, next);
         }