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Commit 6c9076ec authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds
Browse files

[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: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent fbb9ce95

kernel/lockdep.c

+2 −3
Original line number Diff line number Diff line
@@ -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);

	}

lib/locking-selftest.c

+4 −4
Original line number Diff line number Diff line
@@ -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");