/*
* 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);
* ...
#include <linux/spinlock.h>
#include <linux/preempt.h>
+#include <linux/lockdep.h>
#include <asm/processor.h>
/*
*/
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)
return ret;
}
+/**
+ * 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
*/
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);
}
/**
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;
}
* 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++;
}
*/
#define __SEQLOCK_UNLOCKED(lockname) \
{ \
- .seqcount = SEQCNT_ZERO, \
+ .seqcount = SEQCNT_ZERO(lockname), \
.lock = __SPIN_LOCK_UNLOCKED(lockname) \
}
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 */
projects / ~andy / linux / blobdiff