diff options
Diffstat (limited to 'include/linux/rwsem.h')
| -rw-r--r-- | include/linux/rwsem.h | 216 |
1 files changed, 187 insertions, 29 deletions
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index 0616ffe45702..f1aaf676a874 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -1,3 +1,4 @@ +/* SPDX-License-Identifier: GPL-2.0 */ /* rwsem.h: R/W semaphores, public interface * * Written by David Howells (dhowells@redhat.com). @@ -10,55 +11,101 @@ #include <linux/linkage.h> #include <linux/types.h> -#include <linux/kernel.h> #include <linux/list.h> #include <linux/spinlock.h> - #include <linux/atomic.h> +#include <linux/err.h> +#include <linux/cleanup.h> -struct rw_semaphore; - -#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK -#include <linux/rwsem-spinlock.h> /* use a generic implementation */ +#ifdef CONFIG_DEBUG_LOCK_ALLOC +# define __RWSEM_DEP_MAP_INIT(lockname) \ + .dep_map = { \ + .name = #lockname, \ + .wait_type_inner = LD_WAIT_SLEEP, \ + }, #else -/* All arch specific implementations share the same struct */ +# define __RWSEM_DEP_MAP_INIT(lockname) +#endif + +#ifndef CONFIG_PREEMPT_RT + +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER +#include <linux/osq_lock.h> +#endif + +/* + * For an uncontended rwsem, count and owner are the only fields a task + * needs to touch when acquiring the rwsem. So they are put next to each + * other to increase the chance that they will share the same cacheline. + * + * In a contended rwsem, the owner is likely the most frequently accessed + * field in the structure as the optimistic waiter that holds the osq lock + * will spin on owner. For an embedded rwsem, other hot fields in the + * containing structure should be moved further away from the rwsem to + * reduce the chance that they will share the same cacheline causing + * cacheline bouncing problem. + */ struct rw_semaphore { - long count; - raw_spinlock_t wait_lock; - struct list_head wait_list; + atomic_long_t count; + /* + * Write owner or one of the read owners as well flags regarding + * the current state of the rwsem. Can be used as a speculative + * check to see if the write owner is running on the cpu. + */ + atomic_long_t owner; +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER + struct optimistic_spin_queue osq; /* spinner MCS lock */ +#endif + raw_spinlock_t wait_lock; + struct list_head wait_list; +#ifdef CONFIG_DEBUG_RWSEMS + void *magic; +#endif #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif }; -extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); -extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); -extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *); -extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); +#define RWSEM_UNLOCKED_VALUE 0UL +#define RWSEM_WRITER_LOCKED (1UL << 0) +#define __RWSEM_COUNT_INIT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) -/* Include the arch specific part */ -#include <asm/rwsem.h> - -/* In all implementations count != 0 means locked */ static inline int rwsem_is_locked(struct rw_semaphore *sem) { - return sem->count != 0; + return atomic_long_read(&sem->count) != RWSEM_UNLOCKED_VALUE; } -#endif +static inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem) +{ + WARN_ON(atomic_long_read(&sem->count) == RWSEM_UNLOCKED_VALUE); +} + +static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem) +{ + WARN_ON(!(atomic_long_read(&sem->count) & RWSEM_WRITER_LOCKED)); +} /* Common initializer macros and functions */ -#ifdef CONFIG_DEBUG_LOCK_ALLOC -# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } +#ifdef CONFIG_DEBUG_RWSEMS +# define __RWSEM_DEBUG_INIT(lockname) .magic = &lockname, #else -# define __RWSEM_DEP_MAP_INIT(lockname) +# define __RWSEM_DEBUG_INIT(lockname) +#endif + +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER +#define __RWSEM_OPT_INIT(lockname) .osq = OSQ_LOCK_UNLOCKED, +#else +#define __RWSEM_OPT_INIT(lockname) #endif -#define __RWSEM_INITIALIZER(name) \ - { RWSEM_UNLOCKED_VALUE, \ - __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \ - LIST_HEAD_INIT((name).wait_list) \ +#define __RWSEM_INITIALIZER(name) \ + { __RWSEM_COUNT_INIT(name), \ + .owner = ATOMIC_LONG_INIT(0), \ + __RWSEM_OPT_INIT(name) \ + .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),\ + .wait_list = LIST_HEAD_INIT((name).wait_list), \ + __RWSEM_DEBUG_INIT(name) \ __RWSEM_DEP_MAP_INIT(name) } #define DECLARE_RWSEM(name) \ @@ -75,9 +122,107 @@ do { \ } while (0) /* + * This is the same regardless of which rwsem implementation that is being used. + * It is just a heuristic meant to be called by somebody already holding the + * rwsem to see if somebody from an incompatible type is wanting access to the + * lock. + */ +static inline int rwsem_is_contended(struct rw_semaphore *sem) +{ + return !list_empty(&sem->wait_list); +} + +#if defined(CONFIG_DEBUG_RWSEMS) || defined(CONFIG_DETECT_HUNG_TASK_BLOCKER) +/* + * Return just the real task structure pointer of the owner + */ +extern struct task_struct *rwsem_owner(struct rw_semaphore *sem); + +/* + * Return true if the rwsem is owned by a reader. + */ +extern bool is_rwsem_reader_owned(struct rw_semaphore *sem); +#endif + +#else /* !CONFIG_PREEMPT_RT */ + +#include <linux/rwbase_rt.h> + +struct rw_semaphore { + struct rwbase_rt rwbase; +#ifdef CONFIG_DEBUG_LOCK_ALLOC + struct lockdep_map dep_map; +#endif +}; + +#define __RWSEM_INITIALIZER(name) \ + { \ + .rwbase = __RWBASE_INITIALIZER(name), \ + __RWSEM_DEP_MAP_INIT(name) \ + } + +#define DECLARE_RWSEM(lockname) \ + struct rw_semaphore lockname = __RWSEM_INITIALIZER(lockname) + +extern void __init_rwsem(struct rw_semaphore *rwsem, const char *name, + struct lock_class_key *key); + +#define init_rwsem(sem) \ +do { \ + static struct lock_class_key __key; \ + \ + __init_rwsem((sem), #sem, &__key); \ +} while (0) + +static __always_inline int rwsem_is_locked(const struct rw_semaphore *sem) +{ + return rw_base_is_locked(&sem->rwbase); +} + +static __always_inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem) +{ + WARN_ON(!rwsem_is_locked(sem)); +} + +static __always_inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem) +{ + WARN_ON(!rw_base_is_write_locked(&sem->rwbase)); +} + +static __always_inline int rwsem_is_contended(struct rw_semaphore *sem) +{ + return rw_base_is_contended(&sem->rwbase); +} + +#endif /* CONFIG_PREEMPT_RT */ + +/* + * The functions below are the same for all rwsem implementations including + * the RT specific variant. + */ + +static inline void rwsem_assert_held(const struct rw_semaphore *sem) +{ + if (IS_ENABLED(CONFIG_LOCKDEP)) + lockdep_assert_held(sem); + else + rwsem_assert_held_nolockdep(sem); +} + +static inline void rwsem_assert_held_write(const struct rw_semaphore *sem) +{ + if (IS_ENABLED(CONFIG_LOCKDEP)) + lockdep_assert_held_write(sem); + else + rwsem_assert_held_write_nolockdep(sem); +} + +/* * lock for reading */ extern void down_read(struct rw_semaphore *sem); +extern int __must_check down_read_interruptible(struct rw_semaphore *sem); +extern int __must_check down_read_killable(struct rw_semaphore *sem); /* * trylock for reading -- returns 1 if successful, 0 if contention @@ -88,6 +233,7 @@ extern int down_read_trylock(struct rw_semaphore *sem); * lock for writing */ extern void down_write(struct rw_semaphore *sem); +extern int __must_check down_write_killable(struct rw_semaphore *sem); /* * trylock for writing -- returns 1 if successful, 0 if contention @@ -104,6 +250,14 @@ extern void up_read(struct rw_semaphore *sem); */ extern void up_write(struct rw_semaphore *sem); +DEFINE_GUARD(rwsem_read, struct rw_semaphore *, down_read(_T), up_read(_T)) +DEFINE_GUARD_COND(rwsem_read, _try, down_read_trylock(_T)) +DEFINE_GUARD_COND(rwsem_read, _intr, down_read_interruptible(_T), _RET == 0) + +DEFINE_GUARD(rwsem_write, struct rw_semaphore *, down_write(_T), up_write(_T)) +DEFINE_GUARD_COND(rwsem_write, _try, down_write_trylock(_T)) +DEFINE_GUARD_COND(rwsem_write, _kill, down_write_killable(_T), _RET == 0) + /* * downgrade write lock to read lock */ @@ -121,17 +275,19 @@ extern void downgrade_write(struct rw_semaphore *sem); * static then another method for expressing nested locking is * the explicit definition of lock class keys and the use of * lockdep_set_class() at lock initialization time. - * See Documentation/lockdep-design.txt for more details.) + * See Documentation/locking/lockdep-design.rst for more details.) */ extern void down_read_nested(struct rw_semaphore *sem, int subclass); +extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass); extern void down_write_nested(struct rw_semaphore *sem, int subclass); +extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass); extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); # define down_write_nest_lock(sem, nest_lock) \ do { \ typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ _down_write_nest_lock(sem, &(nest_lock)->dep_map); \ -} while (0); +} while (0) /* * Take/release a lock when not the owner will release it. @@ -143,8 +299,10 @@ extern void down_read_non_owner(struct rw_semaphore *sem); extern void up_read_non_owner(struct rw_semaphore *sem); #else # define down_read_nested(sem, subclass) down_read(sem) +# define down_read_killable_nested(sem, subclass) down_read_killable(sem) # define down_write_nest_lock(sem, nest_lock) down_write(sem) # define down_write_nested(sem, subclass) down_write(sem) +# define down_write_killable_nested(sem, subclass) down_write_killable(sem) # define down_read_non_owner(sem) down_read(sem) # define up_read_non_owner(sem) up_read(sem) #endif |