diff options
Diffstat (limited to 'include/linux/seqlock.h')
| -rw-r--r-- | include/linux/seqlock.h | 176 |
1 files changed, 164 insertions, 12 deletions
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index 18299057402f..cf87a24c0f92 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -3,15 +3,21 @@ /* * Reader/writer consistent mechanism without starving writers. This type of * lock for data where the reader wants a consistent set of information - * and is willing to retry if the information changes. Readers never - * block but they may have to retry if a writer is in - * progress. Writers do not wait for readers. + * and is willing to retry if the information changes. There are two types + * of readers: + * 1. Sequence readers which never block a writer but they may have to retry + * if a writer is in progress by detecting change in sequence number. + * Writers do not wait for a sequence reader. + * 2. Locking readers which will wait if a writer or another locking reader + * is in progress. A locking reader in progress will also block a writer + * from going forward. Unlike the regular rwlock, the read lock here is + * exclusive so that only one locking reader can get it. * - * This is not as cache friendly as brlock. Also, this will not work + * This is not as cache friendly as brlock. Also, this may not work well * for data that contains pointers, because any writer could * invalidate a pointer that a reader was following. * - * Expected reader usage: + * Expected non-blocking reader usage: * do { * seq = read_seqbegin(&foo); * ... @@ -28,6 +34,7 @@ #include <linux/spinlock.h> #include <linux/preempt.h> +#include <linux/lockdep.h> #include <asm/processor.h> /* @@ -38,10 +45,50 @@ */ typedef struct seqcount { unsigned sequence; +#ifdef CONFIG_DEBUG_LOCK_ALLOC + struct lockdep_map dep_map; +#endif } seqcount_t; -#define SEQCNT_ZERO { 0 } -#define seqcount_init(x) do { *(x) = (seqcount_t) SEQCNT_ZERO; } while (0) +static inline void __seqcount_init(seqcount_t *s, const char *name, + struct lock_class_key *key) +{ + /* + * Make sure we are not reinitializing a held lock: + */ + lockdep_init_map(&s->dep_map, name, key, 0); + s->sequence = 0; +} + +#ifdef CONFIG_DEBUG_LOCK_ALLOC +# define SEQCOUNT_DEP_MAP_INIT(lockname) \ + .dep_map = { .name = #lockname } \ + +# define seqcount_init(s) \ + do { \ + static struct lock_class_key __key; \ + __seqcount_init((s), #s, &__key); \ + } while (0) + +static inline void seqcount_lockdep_reader_access(const seqcount_t *s) +{ + seqcount_t *l = (seqcount_t *)s; + unsigned long flags; + + local_irq_save(flags); + seqcount_acquire_read(&l->dep_map, 0, 0, _RET_IP_); + seqcount_release(&l->dep_map, 1, _RET_IP_); + local_irq_restore(flags); +} + +#else +# define SEQCOUNT_DEP_MAP_INIT(lockname) +# define seqcount_init(s) __seqcount_init(s, NULL, NULL) +# define seqcount_lockdep_reader_access(x) +#endif + +#define SEQCNT_ZERO(lockname) { .sequence = 0, SEQCOUNT_DEP_MAP_INIT(lockname)} + /** * __read_seqcount_begin - begin a seq-read critical section (without barrier) @@ -70,6 +117,22 @@ repeat: } /** + * read_seqcount_begin_no_lockdep - start seq-read critical section w/o lockdep + * @s: pointer to seqcount_t + * Returns: count to be passed to read_seqcount_retry + * + * read_seqcount_begin_no_lockdep opens a read critical section of the given + * seqcount, but without any lockdep checking. Validity of the critical + * section is tested by checking read_seqcount_retry function. + */ +static inline unsigned read_seqcount_begin_no_lockdep(const seqcount_t *s) +{ + unsigned ret = __read_seqcount_begin(s); + smp_rmb(); + return ret; +} + +/** * read_seqcount_begin - begin a seq-read critical section * @s: pointer to seqcount_t * Returns: count to be passed to read_seqcount_retry @@ -80,9 +143,8 @@ repeat: */ static inline unsigned read_seqcount_begin(const seqcount_t *s) { - unsigned ret = __read_seqcount_begin(s); - smp_rmb(); - return ret; + seqcount_lockdep_reader_access(s); + return read_seqcount_begin_no_lockdep(s); } /** @@ -102,6 +164,8 @@ static inline unsigned read_seqcount_begin(const seqcount_t *s) static inline unsigned raw_seqcount_begin(const seqcount_t *s) { unsigned ret = ACCESS_ONCE(s->sequence); + + seqcount_lockdep_reader_access(s); smp_rmb(); return ret & ~1; } @@ -146,14 +210,21 @@ static inline int read_seqcount_retry(const seqcount_t *s, unsigned start) * Sequence counter only version assumes that callers are using their * own mutexing. */ -static inline void write_seqcount_begin(seqcount_t *s) +static inline void write_seqcount_begin_nested(seqcount_t *s, int subclass) { s->sequence++; smp_wmb(); + seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_); +} + +static inline void write_seqcount_begin(seqcount_t *s) +{ + write_seqcount_begin_nested(s, 0); } static inline void write_seqcount_end(seqcount_t *s) { + seqcount_release(&s->dep_map, 1, _RET_IP_); smp_wmb(); s->sequence++; } @@ -182,7 +253,7 @@ typedef struct { */ #define __SEQLOCK_UNLOCKED(lockname) \ { \ - .seqcount = SEQCNT_ZERO, \ + .seqcount = SEQCNT_ZERO(lockname), \ .lock = __SPIN_LOCK_UNLOCKED(lockname) \ } @@ -268,4 +339,85 @@ write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags) spin_unlock_irqrestore(&sl->lock, flags); } +/* + * A locking reader exclusively locks out other writers and locking readers, + * but doesn't update the sequence number. Acts like a normal spin_lock/unlock. + * Don't need preempt_disable() because that is in the spin_lock already. + */ +static inline void read_seqlock_excl(seqlock_t *sl) +{ + spin_lock(&sl->lock); +} + +static inline void read_sequnlock_excl(seqlock_t *sl) +{ + spin_unlock(&sl->lock); +} + +/** + * read_seqbegin_or_lock - begin a sequence number check or locking block + * @lock: sequence lock + * @seq : sequence number to be checked + * + * First try it once optimistically without taking the lock. If that fails, + * take the lock. The sequence number is also used as a marker for deciding + * whether to be a reader (even) or writer (odd). + * N.B. seq must be initialized to an even number to begin with. + */ +static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq) +{ + if (!(*seq & 1)) /* Even */ + *seq = read_seqbegin(lock); + else /* Odd */ + read_seqlock_excl(lock); +} + +static inline int need_seqretry(seqlock_t *lock, int seq) +{ + return !(seq & 1) && read_seqretry(lock, seq); +} + +static inline void done_seqretry(seqlock_t *lock, int seq) +{ + if (seq & 1) + read_sequnlock_excl(lock); +} + +static inline void read_seqlock_excl_bh(seqlock_t *sl) +{ + spin_lock_bh(&sl->lock); +} + +static inline void read_sequnlock_excl_bh(seqlock_t *sl) +{ + spin_unlock_bh(&sl->lock); +} + +static inline void read_seqlock_excl_irq(seqlock_t *sl) +{ + spin_lock_irq(&sl->lock); +} + +static inline void read_sequnlock_excl_irq(seqlock_t *sl) +{ + spin_unlock_irq(&sl->lock); +} + +static inline unsigned long __read_seqlock_excl_irqsave(seqlock_t *sl) +{ + unsigned long flags; + + spin_lock_irqsave(&sl->lock, flags); + return flags; +} + +#define read_seqlock_excl_irqsave(lock, flags) \ + do { flags = __read_seqlock_excl_irqsave(lock); } while (0) + +static inline void +read_sequnlock_excl_irqrestore(seqlock_t *sl, unsigned long flags) +{ + spin_unlock_irqrestore(&sl->lock, flags); +} + #endif /* __LINUX_SEQLOCK_H */ |