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SubjectRe: [PATCH -tip] locking/rwsem: Check for operations on an uninitialized rwsem
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On 7/29/19 12:47 AM, Davidlohr Bueso wrote:
> Currently rwsems is the only locking primitive that lacks this
> debug feature. Add it under CONFIG_DEBUG_RWSEMS and do the magic
> checking in the locking fastpath (trylock) operation such that
> we cover all cases. The unlocking part is pretty straightforward.
>
> Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
> ---
> include/linux/rwsem.h | 10 ++++++++++
> kernel/locking/rwsem.c | 22 ++++++++++++++++++----
> 2 files changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
> index 9d9c663987d8..00d6054687dd 100644
> --- a/include/linux/rwsem.h
> +++ b/include/linux/rwsem.h
> @@ -45,6 +45,9 @@ struct rw_semaphore {
> #endif
> raw_spinlock_t wait_lock;
> struct list_head wait_list;
> +#ifdef CONFIG_DEBUG_RWSEMS
> + void *magic;
> +#endif
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
> struct lockdep_map dep_map;
> #endif
> @@ -73,6 +76,12 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
> # define __RWSEM_DEP_MAP_INIT(lockname)
> #endif
>
> +#ifdef CONFIG_DEBUG_RWSEMS
> +# define __DEBUG_RWSEM_INITIALIZER(lockname) , .magic = &lockname
> +#else
> +# define __DEBUG_RWSEM_INITIALIZER(lockname)
> +#endif
> +
> #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
> #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED
> #else
> @@ -85,6 +94,7 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
> .wait_list = LIST_HEAD_INIT((name).wait_list), \
> .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
> __RWSEM_OPT_INIT(name) \
> + __DEBUG_RWSEM_INITIALIZER(name) \
> __RWSEM_DEP_MAP_INIT(name) }
>
> #define DECLARE_RWSEM(name) \
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index 37524a47f002..ab392ec51252 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -105,8 +105,9 @@
> #ifdef CONFIG_DEBUG_RWSEMS
> # define DEBUG_RWSEMS_WARN_ON(c, sem) do { \
> if (!debug_locks_silent && \
> - WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
> + WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
> #c, atomic_long_read(&(sem)->count), \
> + (unsigned long) sem->magic, \
> atomic_long_read(&(sem)->owner), (long)current, \
> list_empty(&(sem)->wait_list) ? "" : "not ")) \
> debug_locks_off(); \
> @@ -329,6 +330,9 @@ void __init_rwsem(struct rw_semaphore *sem, const char *name,
> */
> debug_check_no_locks_freed((void *)sem, sizeof(*sem));
> lockdep_init_map(&sem->dep_map, name, key, 0);
> +#endif
> +#ifdef CONFIG_DEBUG_RWSEMS
> + sem->magic = sem;
> #endif
> atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
> raw_spin_lock_init(&sem->wait_lock);
> @@ -1322,11 +1326,14 @@ static inline int __down_read_killable(struct rw_semaphore *sem)
>
> static inline int __down_read_trylock(struct rw_semaphore *sem)
> {
> + long tmp;
> +
> + DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
> +
> /*
> * Optimize for the case when the rwsem is not locked at all.
> */
> - long tmp = RWSEM_UNLOCKED_VALUE;
> -
> + tmp = RWSEM_UNLOCKED_VALUE;
> do {
> if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
> tmp + RWSEM_READER_BIAS)) {
> @@ -1367,8 +1374,11 @@ static inline int __down_write_killable(struct rw_semaphore *sem)
>
> static inline int __down_write_trylock(struct rw_semaphore *sem)
> {
> - long tmp = RWSEM_UNLOCKED_VALUE;
> + long tmp;
>
> + DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
> +
> + tmp = RWSEM_UNLOCKED_VALUE;
> if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
> RWSEM_WRITER_LOCKED)) {
> rwsem_set_owner(sem);
> @@ -1384,7 +1394,9 @@ inline void __up_read(struct rw_semaphore *sem)
> {
> long tmp;
>
> + DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
> DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
> +
> rwsem_clear_reader_owned(sem);
> tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
> DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
> @@ -1402,12 +1414,14 @@ static inline void __up_write(struct rw_semaphore *sem)
> {
> long tmp;
>
> + DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
> /*
> * sem->owner may differ from current if the ownership is transferred
> * to an anonymous writer by setting the RWSEM_NONSPINNABLE bits.
> */
> DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) &&
> !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);
> +
> rwsem_clear_owner(sem);
> tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
> if (unlikely(tmp & RWSEM_FLAG_WAITERS))

Acked-by:  Waiman Long <longman@redhat.com>

Thanks for the patch.
-Longman

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