[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>

2 files changed, 6 insertions, 7 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);
         }
diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index 9bdc8d440b2b..7945787f439a 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -248,7 +248,7 @@ GENERATE_TESTCASE(AA_rsem)
 
 /*
  * Special-case for read-locking, they are
- * allowed to recurse on the same lock instance:
+ * allowed to recurse on the same lock class:
  */
 static void rlock_AA1(void)
 {
@@ -259,7 +259,7 @@ static void rlock_AA1(void)
 static void rlock_AA1B(void)
 {
         RL(X1);
-        RL(X2); // this one should fail
+        RL(X2); // this one should NOT fail
 }
 
 static void rsem_AA1(void)
@@ -1132,7 +1132,7 @@ void locking_selftest(void)
         init_shared_classes();
         debug_locks_silent = !debug_locks_verbose;
 
-        DO_TESTCASE_6("A-A deadlock", AA);
+        DO_TESTCASE_6R("A-A deadlock", AA);
         DO_TESTCASE_6R("A-B-B-A deadlock", ABBA);
         DO_TESTCASE_6R("A-B-B-C-C-A deadlock", ABBCCA);
         DO_TESTCASE_6R("A-B-C-A-B-C deadlock", ABCABC);
@@ -1153,7 +1153,7 @@ void locking_selftest(void)
 
         print_testname("recursive read-lock #2");
         printk("             |");
-        dotest(rlock_AA1B, FAILURE, LOCKTYPE_RWLOCK);
+        dotest(rlock_AA1B, SUCCESS, LOCKTYPE_RWLOCK);
         printk("             |");
         dotest(rsem_AA1B, FAILURE, LOCKTYPE_RWSEM);
         printk("\n");