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SubjectRe: [PATCH v4 3/5] locking/rwsem: Change waiter->hanodff_set to a handoff_state enum
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On 10/24/22 12:44 PM, Waiman Long wrote:
> Change the boolean waiter->handoff_set to an enum type so that we can
> have more states in some later patches. Also use READ_ONCE() outside
> wait_lock critical sections for read and WRITE_ONCE() inside wait_lock
> critical sections for write for proper synchronization. There is no
> functional change.

Hi,

Do we need


Fixes: d257cc8cb8d5 ("locking/rwsem: Make handoff bit handling more
consistent")

Fixes: 91d2a812dfb9 ("locking/rwsem: Make handoff writer optimistically
spin on owner")

Cc: stable@vger.kernel.org


clauses added to patches 3,4,5 so they are all picked up in one series ?

Thank you,

John.



>
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> kernel/locking/rwsem.c | 21 +++++++++++++--------
> 1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index c68d76fc8c68..a8bfc905637a 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -338,12 +338,17 @@ enum rwsem_waiter_type {
> RWSEM_WAITING_FOR_READ
> };
>
> +enum rwsem_handoff_state {
> + HANDOFF_NONE = 0,
> + HANDOFF_REQUESTED,
> +};
> +
> struct rwsem_waiter {
> struct list_head list;
> struct task_struct *task;
> enum rwsem_waiter_type type;
> + enum rwsem_handoff_state handoff_state;
> unsigned long timeout;
> - bool handoff_set;
> };
> #define rwsem_first_waiter(sem) \
> list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
> @@ -470,7 +475,7 @@ static void rwsem_mark_wake(struct rw_semaphore *sem,
> adjustment -= RWSEM_FLAG_HANDOFF;
> lockevent_inc(rwsem_rlock_handoff);
> }
> - waiter->handoff_set = true;
> + WRITE_ONCE(waiter->handoff_state, HANDOFF_REQUESTED);
> }
>
> atomic_long_add(-adjustment, &sem->count);
> @@ -622,7 +627,7 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
> * waiter is the one that set it. Otherwisee, we
> * still try to acquire the rwsem.
> */
> - if (first->handoff_set && (waiter != first))
> + if (first->handoff_state && (waiter != first))
> return false;
> }
>
> @@ -650,11 +655,11 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
>
> /*
> * We have either acquired the lock with handoff bit cleared or set
> - * the handoff bit. Only the first waiter can have its handoff_set
> + * the handoff bit. Only the first waiter can have its handoff_state
> * set here to enable optimistic spinning in slowpath loop.
> */
> if (new & RWSEM_FLAG_HANDOFF) {
> - first->handoff_set = true;
> + WRITE_ONCE(first->handoff_state, HANDOFF_REQUESTED);
> lockevent_inc(rwsem_wlock_handoff);
> return false;
> }
> @@ -1043,7 +1048,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat
> waiter.task = current;
> waiter.type = RWSEM_WAITING_FOR_READ;
> waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
> - waiter.handoff_set = false;
> + waiter.handoff_state = HANDOFF_NONE;
>
> raw_spin_lock_irq(&sem->wait_lock);
> if (list_empty(&sem->wait_list)) {
> @@ -1131,7 +1136,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
> waiter.task = current;
> waiter.type = RWSEM_WAITING_FOR_WRITE;
> waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
> - waiter.handoff_set = false;
> + waiter.handoff_state = HANDOFF_NONE;
>
> raw_spin_lock_irq(&sem->wait_lock);
> rwsem_add_waiter(sem, &waiter);
> @@ -1176,7 +1181,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
> * In this case, we attempt to acquire the lock again
> * without sleeping.
> */
> - if (waiter.handoff_set) {
> + if (READ_ONCE(waiter.handoff_state)) {
> enum owner_state owner_state;
>
> preempt_disable();

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