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SubjectRe: [PATCH] locking/pvqspinlock: Fix kernel panic in locking-selftest
On 2015/07/12 10:19, Waiman Long wrote:
> 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.
>

OK, I've tested this with make allmodconfig && make localmodconfig kernel.
(I've hit another issue to boot, but it seems not related to this issue)

Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

Thank you!



> 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.
>


--
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@hitachi.com


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