On Wed, Mar 01, 2017 at 11:01:38PM +0800, Boqun Feng wrote:
>
> In test-ww_mutex, the stress will use 4096 locks to do the test, and
> given held_lock::references only have 12 bits, so I think this is the
> reason? I made a patch to reduce the lock number of stress test, and it
> seems the problem is resolved.
>
> Thoughts?
Aaaahhh!! YES. I completely overlooked (and forgot) ww_mutex used that.
Let me also do a lockdep patch that complains on overflow there.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 5 at ../kernel/locking/lockdep.c:3269
__lock_acquire.isra.7+0xf8/0x703
DEBUG_LOCKS_WARN_ON(hlock->references == (1 << 12)-1)
CPU: 0 PID: 5 Comm: kworker/u2:0 Not tainted 4.10.0-01418-gfba4873-dirty #29
Workqueue: test-ww_mutex stress_inorder_work
Call Trace:
dump_stack+0x16/0x18
__warn+0xa0/0xb7
? __lock_acquire.isra.7+0xf8/0x703
warn_slowpath_fmt+0x28/0x2d
__lock_acquire.isra.7+0xf8/0x703
lock_acquire+0x6c/0x95
? stress_inorder_work+0xbf/0x218
__ww_mutex_lock.constprop.0+0x5c/0x848
? stress_inorder_work+0xbf/0x218
? __might_sleep+0x6c/0x73
ww_mutex_lock+0x34/0x3b
? stress_inorder_work+0xbf/0x218
stress_inorder_work+0xbf/0x218
process_one_work+0x1c0/0x33a
? process_one_work+0x168/0x33a
worker_thread+0x22f/0x315
kthread+0xed/0xf2
? process_scheduled_works+0x24/0x24
? __kthread_create_on_node+0x11f/0x11f
ret_from_fork+0x21/0x30
---[ end trace 326b6bfcd7100ae8 ]---
---
kernel/locking/lockdep.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 9812e5dd409e..c0ee8607c11e 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3260,10 +3260,17 @@ static int __lock_acquire(struct lockdep_map *lock,
unsigned int subclass,
if (depth) {
hlock = curr->held_locks + depth - 1;
if (hlock->class_idx == class_idx && nest_lock) {
- if (hlock->references)
+ if (hlock->references) {
+ /*
+ * Check: unsigned int references:12, overflow.
+ */
+ if (DEBUG_LOCKS_WARN_ON(hlock->references == (1
<< 12)-1))
+ return 0;
+
hlock->references++;
- else
+ } else {
hlock->references = 2;
+ }
return 1;
}
