Re: [PATCH 2/3] rwsem: Implement down_read_interruptible

Eric W. Biederman
2020-12-07T15:58:10Z

Peter Zijlstra <peterz@infradead.org> writes:

> On Thu, Dec 03, 2020 at 08:59:13PM -0500, Waiman Long wrote:
>> On 12/3/20 3:11 PM, Eric W. Biederman wrote:
>
>> > +static inline int __down_read_interruptible(struct rw_semaphore *sem)
>> > +{
>> > + if (!rwsem_read_trylock(sem)) {
>> > + if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_INTERRUPTIBLE)))
>> > + return -EINTR;
>> > + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
>> > + } else {
>> > + rwsem_set_reader_owned(sem);
>> > + }
>> > + return 0;
>> > +}
>> > +
>> > static inline int __down_read_killable(struct rw_semaphore *sem)
>> > {
>> > if (!rwsem_read_trylock(sem)) {
>> > @@ -1495,6 +1507,20 @@ void __sched down_read(struct rw_semaphore *sem)
>> > }
>> > EXPORT_SYMBOL(down_read);
>> > +int __sched down_read_interruptible(struct rw_semaphore *sem)
>> > +{
>> > + might_sleep();
>> > + rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
>> > +
>> > + if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
>> > + rwsem_release(&sem->dep_map, _RET_IP_);
>> > + return -EINTR;
>> > + }
>> > +
>> > + return 0;
>> > +}
>> > +EXPORT_SYMBOL(down_read_interruptible);
>> > +
>> > int __sched down_read_killable(struct rw_semaphore *sem)
>> > {
>> > might_sleep();
>>
>> Acked-by: Waiman Long <longman@redhat.com>
>
> Yeah, that seems correct.. There's an unfortunate amount of copy-paste
> there though.
>
> Do we want to follow that up with something like this?

Do you want to pull these two into a topic branch in the tip tree
based on v10-rc1?

That way we can share these two patches, and then you folks can make
your locking cleanups and I can change exec_update_mutex to a rw_semaphore?

Eric

> ---
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -275,7 +275,25 @@ static inline bool rwsem_read_trylock(st
> long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
> if (WARN_ON_ONCE(cnt < 0))
> rwsem_set_nonspinnable(sem);
> - return !(cnt & RWSEM_READ_FAILED_MASK);
> +
> + if (!(cnt & RWSEM_READ_FAILED_MASK)) {
> + rwsem_set_reader_owned(sem);
> + return true;
> + }
> +
> + return false;
> +}
> +
> +static inline bool rwsem_write_trylock(struct rw_semaphore *sem)
> +{
> + long tmp = RWSEM_UNLOCKED_VALUE;
> +
> + if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {
> + rwsem_set_owner(sem);
> + return true;
> + }
> +
> + return false;
> }
>
> /*
> @@ -1335,38 +1353,29 @@ static struct rw_semaphore *rwsem_downgr
> /*
> * lock for reading
> */
> -static inline void __down_read(struct rw_semaphore *sem)
> +static inline int __down_read_common(struct rw_semaphore *sem, int state)
> {
> if (!rwsem_read_trylock(sem)) {
> - rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE);
> + if (IS_ERR(rwsem_down_read_slowpath(sem, state)))
> + return -EINTR;
> DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
> - } else {
> - rwsem_set_reader_owned(sem);
> }
> + return 0;
> }
>
> -static inline int __down_read_interruptible(struct rw_semaphore *sem)
> +static __always_inline void __down_read(struct rw_semaphore *sem)
> {
> - if (!rwsem_read_trylock(sem)) {
> - if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_INTERRUPTIBLE)))
> - return -EINTR;
> - DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
> - } else {
> - rwsem_set_reader_owned(sem);
> - }
> - return 0;
> + __down_read_common(sem, TASK_UNINTERRUPTIBLE);
> }
>
> -static inline int __down_read_killable(struct rw_semaphore *sem)
> +static __always_inline int __down_read_interruptible(struct rw_semaphore *sem)
> {
> - if (!rwsem_read_trylock(sem)) {
> - if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE)))
> - return -EINTR;
> - DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
> - } else {
> - rwsem_set_reader_owned(sem);
> - }
> - return 0;
> + return __down_read_common(sem, TASK_INTERRUPTIBLE);
> +}
> +
> +static __always_inline int __down_read_killable(struct rw_semaphore *sem)
> +{
> + return __down_read_common(sem, TASK_KILLABLE);
> }
>
> static inline int __down_read_trylock(struct rw_semaphore *sem)
> @@ -1392,44 +1401,29 @@ static inline int __down_read_trylock(st
> /*
> * lock for writing
> */
> -static inline void __down_write(struct rw_semaphore *sem)
> +static inline int __down_write_common(struct rw_semaphore *sem, int state)
> {
> - long tmp = RWSEM_UNLOCKED_VALUE;
> -
> - if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
> - RWSEM_WRITER_LOCKED)))
> - rwsem_down_write_slowpath(sem, TASK_UNINTERRUPTIBLE);
> - else
> - rwsem_set_owner(sem);
> + if (unlikely(!rwsem_write_trylock(sem))) {
> + if (IS_ERR(rwsem_down_write_slowpath(sem, state)))
> + return -EINTR;
> + }
> + return 0;
> }
>
> -static inline int __down_write_killable(struct rw_semaphore *sem)
> +static __always_inline void __down_write(struct rw_semaphore *sem)
> {
> - long tmp = RWSEM_UNLOCKED_VALUE;
> + __down_write_common(sem, TASK_UNINTERRUPTIBLE);
> +}
>
> - if (unlikely(!atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
> - RWSEM_WRITER_LOCKED))) {
> - if (IS_ERR(rwsem_down_write_slowpath(sem, TASK_KILLABLE)))
> - return -EINTR;
> - } else {
> - rwsem_set_owner(sem);
> - }
> - return 0;
> +static __always_inline int __down_write_killable(struct rw_semaphore *sem)
> +{
> + return __down_write_common(sem, TASK_KILLABLE);
> }
>
> static inline int __down_write_trylock(struct rw_semaphore *sem)
> {
> - 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);
> - return true;
> - }
> - return false;
> + return rwsem_write_trylock(sem);
> }
>
> /*