Re: [PATCH v3 1/2] rtmutex: allow specifying a subclass for nested locking

Joel Fernandes
2018-05-28T05:19:36Z

On Thu, May 24, 2018 at 03:52:39PM +0200, Peter Rosin wrote:
> Needed for annotating rt_mutex locks.
>
> Signed-off-by: Peter Rosin <peda@axentia.se>
> ---
> include/linux/rtmutex.h | 7 +++++++
> kernel/locking/rtmutex.c | 29 +++++++++++++++++++++++++----
> 2 files changed, 32 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/rtmutex.h b/include/linux/rtmutex.h
> index 1b92a28dd672..6fd615a0eea9 100644
> --- a/include/linux/rtmutex.h
> +++ b/include/linux/rtmutex.h
> @@ -106,7 +106,14 @@ static inline int rt_mutex_is_locked(struct rt_mutex *lock)
> extern void __rt_mutex_init(struct rt_mutex *lock, const char *name, struct lock_class_key *key);
> extern void rt_mutex_destroy(struct rt_mutex *lock);
>
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +extern void rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass);
> +#define rt_mutex_lock(lock) rt_mutex_lock_nested(lock, 0)
> +#else
> extern void rt_mutex_lock(struct rt_mutex *lock);
> +#define rt_mutex_lock_nested(lock, subclass) rt_mutex_lock(lock)
> +#endif
> +
> extern int rt_mutex_lock_interruptible(struct rt_mutex *lock);
> extern int rt_mutex_timed_lock(struct rt_mutex *lock,
> struct hrtimer_sleeper *timeout);
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
:
> }
>
> +static inline void __rt_mutex_lock(struct rt_mutex *lock, unsigned int subclass)
> +{
> + might_sleep();
> +
> + mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
> + rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
> +}
> +
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +/**
> + * rt_mutex_lock_nested - lock a rt_mutex

This ifdef seems consistent with other nested locking primitives, but its
kind of confusing.

The Kconfig.debug for DEBUG_LOCK_ALLOC says:

config DEBUG_LOCK_ALLOC
bool "Lock debugging: detect incorrect freeing of live locks"
[...]
help
This feature will check whether any held lock (spinlock, rwlock,
mutex or rwsem) is incorrectly freed by the kernel, via any of the
memory-freeing routines (kfree(), kmem_cache_free(), free_pages(),
vfree(), etc.), whether a live lock is incorrectly reinitialized via
spin_lock_init()/mutex_init()/etc., or whether there is any lock
held during task exit.

Shouldn't this ideally be ifdef'd under PROVE_LOCKING for this and other
locking primitives? Any idea what's the reason? I know PROVE_LOCKING selects
DEBUG_LOCK_ALLOC but still..

thanks!

- Joel