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Subject[PATCH 1/5] locking/rwsem: Pass the current atomic count to rwsem_down_read_slowpath()
Date
The atomic count value right after reader count increment can be useful
to determine the rwsem state at trylock time. So the count value is
passed down to rwsem_down_read_slowpath() to be used when appropriate.

Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/rwsem.c | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index f11b9bd3431d..12761e02ab9b 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -270,12 +270,12 @@ static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
owner | RWSEM_NONSPINNABLE));
}

-static inline bool rwsem_read_trylock(struct rw_semaphore *sem)
+static inline long rwsem_read_trylock(struct rw_semaphore *sem)
{
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);
+ return cnt;
}

/*
@@ -989,9 +989,9 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
* Wait for the read lock to be granted
*/
static struct rw_semaphore __sched *
-rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
+rwsem_down_read_slowpath(struct rw_semaphore *sem, int state, long count)
{
- long count, adjustment = -RWSEM_READER_BIAS;
+ long adjustment = -RWSEM_READER_BIAS;
struct rwsem_waiter waiter;
DEFINE_WAKE_Q(wake_q);
bool wake = false;
@@ -1337,8 +1337,10 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
*/
static inline void __down_read(struct rw_semaphore *sem)
{
- if (!rwsem_read_trylock(sem)) {
- rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE);
+ long count = rwsem_read_trylock(sem);
+
+ if (count & RWSEM_READ_FAILED_MASK) {
+ rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE, count);
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
} else {
rwsem_set_reader_owned(sem);
@@ -1347,8 +1349,10 @@ static inline void __down_read(struct rw_semaphore *sem)

static inline int __down_read_killable(struct rw_semaphore *sem)
{
- if (!rwsem_read_trylock(sem)) {
- if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE)))
+ long count = rwsem_read_trylock(sem);
+
+ if (count & RWSEM_READ_FAILED_MASK) {
+ if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE, count)))
return -EINTR;
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
} else {
--
2.18.1
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