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Subject[PATCH] locking/pvqspinlock: Fix kernel panic in locking-selftest
Date
Enabling locking-selftest in a VM guest may cause the following
kernel panic:

kernel BUG at .../kernel/locking/qspinlock_paravirt.h:137!

This is due to the fact that the pvqspinlock unlock function is
expecting either a _Q_LOCKED_VAL or _Q_SLOW_VAL in the lock byte. This
patch prevents that bug report by ignoring it when debug_locks_silent
is set. Otherwise, a warning will be printed if it contains an
unexpected value.

With this patch applied, the kernel locking-selftest completed without
any noise.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
---
kernel/locking/qspinlock_paravirt.h | 12 +++++++++++-
1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 04ab181..15d3733 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -4,6 +4,7 @@

#include <linux/hash.h>
#include <linux/bootmem.h>
+#include <linux/debug_locks.h>

/*
* Implement paravirt qspinlocks; the general idea is to halt the vcpus instead
@@ -286,15 +287,24 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
{
struct __qspinlock *l = (void *)lock;
struct pv_node *node;
+ u8 lockval = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);

/*
* 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))
+ if (likely(lockval == _Q_LOCKED_VAL))
return;

+ if (unlikely(lockval != _Q_SLOW_VAL)) {
+ if (debug_locks_silent)
+ return;
+ WARN(1, "pvqspinlock: lock 0x%lx has corrupted value 0x%x!\n",
+ (unsigned long)lock, atomic_read(&lock->val));
+ return;
+ }
+
/*
* Since the above failed to release, this must be the SLOW path.
* Therefore start by looking up the blocked node and unhashing it.
--
1.7.1


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