diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index e795908f3607..604d247ea8c3 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -357,11 +357,8 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) rcu_read_lock(); owner = READ_ONCE(sem->owner); - if (!rwsem_owner_is_writer(owner)) { - /* - * Don't spin if the rwsem is readers owned. - */ - ret = !rwsem_owner_is_reader(owner); + if (!owner || !is_rwsem_owner_spinnable(owner)) { + ret = !owner; /* !owner is spinnable */ goto done; } @@ -382,11 +379,11 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) { struct task_struct *owner = READ_ONCE(sem->owner); - if (!rwsem_owner_is_writer(owner)) - goto out; + if (!is_rwsem_owner_spinnable(owner)) + return false; rcu_read_lock(); - while (sem->owner == owner) { + while (owner && (READ_ONCE(sem->owner) == owner)) { /* * Ensure we emit the owner->on_cpu, dereference _after_ * checking sem->owner still matches owner, if that fails, @@ -408,12 +405,12 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) cpu_relax(); } rcu_read_unlock(); -out: + /* * If there is a new owner or the owner is not set, we continue * spinning. */ - return !rwsem_owner_is_reader(READ_ONCE(sem->owner)); + return is_rwsem_owner_spinnable(READ_ONCE(sem->owner)); } static bool rwsem_optimistic_spin(struct rw_semaphore *sem) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 30465a2f2b6c..bc1e507be9ff 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -221,5 +221,3 @@ void up_read_non_owner(struct rw_semaphore *sem) EXPORT_SYMBOL(up_read_non_owner); #endif - - diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h index a17cba8d94bb..b9d0e72aa80f 100644 --- a/kernel/locking/rwsem.h +++ b/kernel/locking/rwsem.h @@ -1,20 +1,24 @@ /* SPDX-License-Identifier: GPL-2.0 */ /* * The owner field of the rw_semaphore structure will be set to - * RWSEM_READ_OWNED when a reader grabs the lock. A writer will clear + * RWSEM_READER_OWNED when a reader grabs the lock. A writer will clear * the owner field when it unlocks. A reader, on the other hand, will * not touch the owner field when it unlocks. * - * In essence, the owner field now has the following 3 states: + * In essence, the owner field now has the following 4 states: * 1) 0 * - lock is free or the owner hasn't set the field yet * 2) RWSEM_READER_OWNED * - lock is currently or previously owned by readers (lock is free * or not set by owner yet) - * 3) Other non-zero value - * - a writer owns the lock + * 3) RWSEM_ANONYMOUSLY_OWNED bit set with some other bits set as well + * - lock is owned by an anonymous writer, so spinning on the lock + * owner should be disabled. + * 4) Other non-zero value + * - a writer owns the lock and other writers can spin on the lock owner. */ -#define RWSEM_READER_OWNED ((struct task_struct *)1UL) +#define RWSEM_ANONYMOUSLY_OWNED (1UL << 0) +#define RWSEM_READER_OWNED ((struct task_struct *)RWSEM_ANONYMOUSLY_OWNED) #ifdef CONFIG_DEBUG_RWSEMS # define DEBUG_RWSEMS_WARN_ON(c) DEBUG_LOCKS_WARN_ON(c) @@ -51,14 +55,22 @@ static inline void rwsem_set_reader_owned(struct rw_semaphore *sem) WRITE_ONCE(sem->owner, RWSEM_READER_OWNED); } -static inline bool rwsem_owner_is_writer(struct task_struct *owner) +/* + * Return true if the a rwsem waiter can spin on the rwsem's owner + * and steal the lock, i.e. the lock is not anonymously owned. + * N.B. !owner is considered spinnable. + */ +static inline bool is_rwsem_owner_spinnable(struct task_struct *owner) { - return owner && owner != RWSEM_READER_OWNED; + return !((unsigned long)owner & RWSEM_ANONYMOUSLY_OWNED); } -static inline bool rwsem_owner_is_reader(struct task_struct *owner) +/* + * Return true if rwsem is owned by an anonymous writer or readers. + */ +static inline bool rwsem_has_anonymous_owner(struct task_struct *owner) { - return owner == RWSEM_READER_OWNED; + return (unsigned long)owner & RWSEM_ANONYMOUSLY_OWNED; } #else static inline void rwsem_set_owner(struct rw_semaphore *sem)