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locking/pvqspinlock: Fix kernel panic in locking-selftest

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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.

Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1436663959-53092-1-git-send-email-Waiman.Long@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Waiman Long 2015-07-11 21:19:19 -04:00 committed by Ingo Molnar
parent 9d634c410b
commit cba77f03f2
1 changed files with 10 additions and 1 deletions
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11
kernel/locking/qspinlock_paravirt.h
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@ -4,6 +4,7 @@
#include <linux/hash.h> #include <linux/hash.h>
#include <linux/bootmem.h> #include <linux/bootmem.h>
#include <linux/debug_locks.h>
/* /*
* Implement paravirt qspinlocks; the general idea is to halt the vcpus instead * Implement paravirt qspinlocks; the general idea is to halt the vcpus instead
@ -286,15 +287,23 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
{ {
struct __qspinlock *l = (void *)lock; struct __qspinlock *l = (void *)lock;
struct pv_node *node; 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 * We must not unlock if SLOW, because in that case we must first
* unhash. Otherwise it would be possible to have multiple @lock * unhash. Otherwise it would be possible to have multiple @lock
* entries, which would be BAD. * entries, which would be BAD.
*/ */
if (likely(cmpxchg(&l->locked, _Q_LOCKED_VAL, 0) == _Q_LOCKED_VAL)) if (likely(lockval == _Q_LOCKED_VAL))
return; return;
if (unlikely(lockval != _Q_SLOW_VAL)) {
if (debug_locks_silent)
return;
WARN(1, "pvqspinlock: lock %p has corrupted value 0x%x!\n", lock, atomic_read(&lock->val));
return;
}
/* /*
* Since the above failed to release, this must be the SLOW path. * Since the above failed to release, this must be the SLOW path.
* Therefore start by looking up the blocked node and unhashing it. * Therefore start by looking up the blocked node and unhashing it.