On Fri, Jul 10, 2015 at 03:57:46PM +0200, Ingo Molnar wrote:
> * Peter Zijlstra <pet...@infradead.org> wrote:
> > Do we want to make double unlock non-fatal unconditionally?
>
> No, just don't BUG() out, don't crash the system - generate a warning?
So that would be a yes..
Something like so then? Won't this generate a splat on that locking self
test then? And upset people?
---
kernel/locking/qspinlock_paravirt.h | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/qspinlock_paravirt.h
b/kernel/locking/qspinlock_paravirt.h
index 04ab18151cc8..286e8978a562 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -133,8 +133,14 @@ static struct pv_node *pv_unhash(struct qspinlock *lock)
* This guarantees a limited lookup time and is itself guaranteed by
* having the lock owner do the unhash -- IFF the unlock sees the
* SLOW flag, there MUST be a hash entry.
+ *
+ * This can trigger due to double-unlock. In which case, return a
+ * random pointer so that __pv_queued_spin_unlock() can dereference it
+ * without crashing.
*/
- BUG();
+ WARN_ON_ONCE(true);
+
+ return (struct pv_node *)this_cpu_ptr(&mcs_nodes[0]);
}
/*
--
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