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

From: Ingo Molnar <[email protected]> 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 <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
diverger · Jul 3, 2006 · 6c9076e · 6c9076e
1 parent fbb9ce9
commit 6c9076e
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Showing 2 changed files with 6 additions and 7 deletions.
diff --git 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
@@ -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");