diff options
| -rw-r--r-- | include/linux/seqlock.h | 68 |
1 files changed, 63 insertions, 5 deletions
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index 18299057402..21a209336e7 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); * ... @@ -268,4 +274,56 @@ 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); +} + +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 */ |