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locking/rwsem: Pass the current atomic count to rwsem_down_read_slowpath()

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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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lkml.kernel.org/r/20201121041416.12285-2-longman@redhat.com
This commit is contained in:
Waiman Long 2020-11-20 23:14:12 -05:00 committed by Peter Zijlstra
parent c995e638cc
commit c8fe8b0564
1 changed files with 10 additions and 8 deletions
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18
kernel/locking/rwsem.c
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@ -270,14 +270,14 @@ 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 bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)
{
long cnt = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
*cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
if (WARN_ON_ONCE(cnt < 0))
if (WARN_ON_ONCE(*cntp < 0))
rwsem_set_nonspinnable(sem);
if (!(cnt & RWSEM_READ_FAILED_MASK)) {
if (!(*cntp & RWSEM_READ_FAILED_MASK)) {
rwsem_set_reader_owned(sem);
return true;
}
@ -1008,9 +1008,9 @@ 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, long count, int state)
{
long count, adjustment = -RWSEM_READER_BIAS;
long adjustment = -RWSEM_READER_BIAS;
struct rwsem_waiter waiter;
DEFINE_WAKE_Q(wake_q);
bool wake = false;
@ -1356,8 +1356,10 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
*/
static inline int __down_read_common(struct rw_semaphore *sem, int state)
{
if (!rwsem_read_trylock(sem)) {
if (IS_ERR(rwsem_down_read_slowpath(sem, state)))
long count;
if (!rwsem_read_trylock(sem, &count)) {
if (IS_ERR(rwsem_down_read_slowpath(sem, count, state)))
return -EINTR;
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
}