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

Peter Zijlstra
2020-12-07T09:03:43Z

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?

---
--- 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);
}

/*