Re: [BUG][tip/master] kernel panic while locking selftest at qspinlock_paravirt.h:137!
From: Peter Zijlstra
Date: Fri Jul 10 2015 - 09:00:46 EST
On Fri, Jul 10, 2015 at 08:32:46PM +0900, Masami Hiramatsu wrote:
> double unlock:
> ------------[ cut here ]------------
> kernel BUG at /home/mhiramat/ksrc/linux-3/kernel/locking/qspinlock_paravirt.h:137!
> Call Trace:
> [<ffffffff81114a59>] __raw_callee_save___pv_queued_spin_unlock+0x11/0x1e
> [<ffffffff81117133>] ? do_raw_spin_unlock+0xfa/0x10c
> [<ffffffff817cd3f7>] _raw_spin_unlock+0x44/0x64
> [<ffffffff814603ee>] double_unlock_spin+0x3d/0x46
Cute, but somewhat expected. A double unlock really is a BUG and the PV
spinlock code cannot deal with it.
Do we want to make double unlock non-fatal unconditionally?
---
kernel/locking/qspinlock_paravirt.h | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 04ab18151cc8..172deeaf1311 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -286,15 +286,22 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
{
struct __qspinlock *l = (void *)lock;
struct pv_node *node;
+ u8 locked;
/*
* We must not unlock if SLOW, because in that case we must first
* unhash. Otherwise it would be possible to have multiple @lock
* entries, which would be BAD.
*/
- if (likely(cmpxchg(&l->locked, _Q_LOCKED_VAL, 0) == _Q_LOCKED_VAL))
+ locked = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
+ if (likely(locked == _Q_LOCKED_VAL))
return;
+#ifdef CONFIG_DEBUG_LOCKING_API_SELFTESTS
+ if (unlikely(!locked))
+ return;
+#endif
+
/*
* Since the above failed to release, this must be the SLOW path.
* Therefore start by looking up the blocked node and unhashing it.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/