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#ifndef __LINUX_SEQLOCK_H |
#define __LINUX_SEQLOCK_H |
/* |
* 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. 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 may not work well |
* for data that contains pointers, because any writer could |
* invalidate a pointer that a reader was following. |
* |
* Expected non-blocking reader usage: |
* do { |
* seq = read_seqbegin(&foo); |
* ... |
* } while (read_seqretry(&foo, seq)); |
* |
* |
* On non-SMP the spin locks disappear but the writer still needs |
* to increment the sequence variables because an interrupt routine could |
* change the state of the data. |
* |
* Based on x86_64 vsyscall gettimeofday |
* by Keith Owens and Andrea Arcangeli |
*/ |
|
#include <linux/spinlock.h> |
//#include <linux/preempt.h> |
#include <linux/lockdep.h> |
#include <asm/processor.h> |
|
/* |
* Version using sequence counter only. |
* This can be used when code has its own mutex protecting the |
* updating starting before the write_seqcountbeqin() and ending |
* after the write_seqcount_end(). |
*/ |
typedef struct seqcount { |
unsigned sequence; |
#ifdef CONFIG_DEBUG_LOCK_ALLOC |
struct lockdep_map dep_map; |
#endif |
} seqcount_t; |
|
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) |
* @s: pointer to seqcount_t |
* Returns: count to be passed to read_seqcount_retry |
* |
* __read_seqcount_begin is like read_seqcount_begin, but has no smp_rmb() |
* barrier. Callers should ensure that smp_rmb() or equivalent ordering is |
* provided before actually loading any of the variables that are to be |
* protected in this critical section. |
* |
* Use carefully, only in critical code, and comment how the barrier is |
* provided. |
*/ |
static inline unsigned __read_seqcount_begin(const seqcount_t *s) |
{ |
unsigned ret; |
|
repeat: |
ret = ACCESS_ONCE(s->sequence); |
if (unlikely(ret & 1)) { |
cpu_relax(); |
goto repeat; |
} |
return ret; |
} |
|
/** |
* raw_read_seqcount - Read the raw seqcount |
* @s: pointer to seqcount_t |
* Returns: count to be passed to read_seqcount_retry |
* |
* raw_read_seqcount opens a read critical section of the given |
* seqcount without any lockdep checking and without checking or |
* masking the LSB. Calling code is responsible for handling that. |
*/ |
static inline unsigned raw_read_seqcount(const seqcount_t *s) |
{ |
unsigned ret = ACCESS_ONCE(s->sequence); |
smp_rmb(); |
return ret; |
} |
|
/** |
* raw_read_seqcount_begin - start seq-read critical section w/o lockdep |
* @s: pointer to seqcount_t |
* Returns: count to be passed to read_seqcount_retry |
* |
* raw_read_seqcount_begin 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 raw_read_seqcount_begin(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 |
* |
* read_seqcount_begin opens a read critical section of the given seqcount. |
* Validity of the critical section is tested by checking read_seqcount_retry |
* function. |
*/ |
static inline unsigned read_seqcount_begin(const seqcount_t *s) |
{ |
seqcount_lockdep_reader_access(s); |
return raw_read_seqcount_begin(s); |
} |
|
/** |
* raw_seqcount_begin - begin a seq-read critical section |
* @s: pointer to seqcount_t |
* Returns: count to be passed to read_seqcount_retry |
* |
* raw_seqcount_begin opens a read critical section of the given seqcount. |
* Validity of the critical section is tested by checking read_seqcount_retry |
* function. |
* |
* Unlike read_seqcount_begin(), this function will not wait for the count |
* to stabilize. If a writer is active when we begin, we will fail the |
* read_seqcount_retry() instead of stabilizing at the beginning of the |
* critical section. |
*/ |
static inline unsigned raw_seqcount_begin(const seqcount_t *s) |
{ |
unsigned ret = ACCESS_ONCE(s->sequence); |
smp_rmb(); |
return ret & ~1; |
} |
|
/** |
* __read_seqcount_retry - end a seq-read critical section (without barrier) |
* @s: pointer to seqcount_t |
* @start: count, from read_seqcount_begin |
* Returns: 1 if retry is required, else 0 |
* |
* __read_seqcount_retry is like read_seqcount_retry, but has no smp_rmb() |
* barrier. Callers should ensure that smp_rmb() or equivalent ordering is |
* provided before actually loading any of the variables that are to be |
* protected in this critical section. |
* |
* Use carefully, only in critical code, and comment how the barrier is |
* provided. |
*/ |
static inline int __read_seqcount_retry(const seqcount_t *s, unsigned start) |
{ |
return unlikely(s->sequence != start); |
} |
|
/** |
* read_seqcount_retry - end a seq-read critical section |
* @s: pointer to seqcount_t |
* @start: count, from read_seqcount_begin |
* Returns: 1 if retry is required, else 0 |
* |
* read_seqcount_retry closes a read critical section of the given seqcount. |
* If the critical section was invalid, it must be ignored (and typically |
* retried). |
*/ |
static inline int read_seqcount_retry(const seqcount_t *s, unsigned start) |
{ |
smp_rmb(); |
return __read_seqcount_retry(s, start); |
} |
|
|
|
static inline void raw_write_seqcount_begin(seqcount_t *s) |
{ |
s->sequence++; |
smp_wmb(); |
} |
|
static inline void raw_write_seqcount_end(seqcount_t *s) |
{ |
smp_wmb(); |
s->sequence++; |
} |
|
/* |
* raw_write_seqcount_latch - redirect readers to even/odd copy |
* @s: pointer to seqcount_t |
*/ |
static inline void raw_write_seqcount_latch(seqcount_t *s) |
{ |
smp_wmb(); /* prior stores before incrementing "sequence" */ |
s->sequence++; |
smp_wmb(); /* increment "sequence" before following stores */ |
} |
|
/* |
* Sequence counter only version assumes that callers are using their |
* own mutexing. |
*/ |
static inline void write_seqcount_begin_nested(seqcount_t *s, int subclass) |
{ |
raw_write_seqcount_begin(s); |
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_); |
raw_write_seqcount_end(s); |
} |
|
/** |
* write_seqcount_barrier - invalidate in-progress read-side seq operations |
* @s: pointer to seqcount_t |
* |
* After write_seqcount_barrier, no read-side seq operations will complete |
* successfully and see data older than this. |
*/ |
static inline void write_seqcount_barrier(seqcount_t *s) |
{ |
smp_wmb(); |
s->sequence+=2; |
} |
|
typedef struct { |
struct seqcount seqcount; |
spinlock_t lock; |
} seqlock_t; |
|
/* |
* These macros triggered gcc-3.x compile-time problems. We think these are |
* OK now. Be cautious. |
*/ |
#define __SEQLOCK_UNLOCKED(lockname) \ |
{ \ |
.seqcount = SEQCNT_ZERO(lockname), \ |
.lock = __SPIN_LOCK_UNLOCKED(lockname) \ |
} |
|
#define seqlock_init(x) \ |
do { \ |
seqcount_init(&(x)->seqcount); \ |
spin_lock_init(&(x)->lock); \ |
} while (0) |
|
#define DEFINE_SEQLOCK(x) \ |
seqlock_t x = __SEQLOCK_UNLOCKED(x) |
|
/* |
* Read side functions for starting and finalizing a read side section. |
*/ |
static inline unsigned read_seqbegin(const seqlock_t *sl) |
{ |
return read_seqcount_begin(&sl->seqcount); |
} |
|
static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start) |
{ |
return read_seqcount_retry(&sl->seqcount, start); |
} |
|
/* |
* Lock out other writers and update the count. |
* Acts like a normal spin_lock/unlock. |
* Don't need preempt_disable() because that is in the spin_lock already. |
*/ |
static inline void write_seqlock(seqlock_t *sl) |
{ |
spin_lock(&sl->lock); |
write_seqcount_begin(&sl->seqcount); |
} |
|
static inline void write_sequnlock(seqlock_t *sl) |
{ |
write_seqcount_end(&sl->seqcount); |
spin_unlock(&sl->lock); |
} |
|
static inline void write_seqlock_bh(seqlock_t *sl) |
{ |
spin_lock_bh(&sl->lock); |
write_seqcount_begin(&sl->seqcount); |
} |
|
static inline void write_sequnlock_bh(seqlock_t *sl) |
{ |
write_seqcount_end(&sl->seqcount); |
spin_unlock_bh(&sl->lock); |
} |
|
static inline void write_seqlock_irq(seqlock_t *sl) |
{ |
spin_lock_irq(&sl->lock); |
write_seqcount_begin(&sl->seqcount); |
} |
|
static inline void write_sequnlock_irq(seqlock_t *sl) |
{ |
write_seqcount_end(&sl->seqcount); |
spin_unlock_irq(&sl->lock); |
} |
|
static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl) |
{ |
unsigned long flags; |
|
spin_lock_irqsave(&sl->lock, flags); |
write_seqcount_begin(&sl->seqcount); |
return flags; |
} |
|
#define write_seqlock_irqsave(lock, flags) \ |
do { flags = __write_seqlock_irqsave(lock); } while (0) |
|
static inline void |
write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags) |
{ |
write_seqcount_end(&sl->seqcount); |
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); |
} |
|
static inline unsigned long |
read_seqbegin_or_lock_irqsave(seqlock_t *lock, int *seq) |
{ |
unsigned long flags = 0; |
|
if (!(*seq & 1)) /* Even */ |
*seq = read_seqbegin(lock); |
else /* Odd */ |
read_seqlock_excl_irqsave(lock, flags); |
|
return flags; |
} |
|
static inline void |
done_seqretry_irqrestore(seqlock_t *lock, int seq, unsigned long flags) |
{ |
if (seq & 1) |
read_sequnlock_excl_irqrestore(lock, flags); |
} |
#endif /* __LINUX_SEQLOCK_H */ |