![John Stultz](/assets/img/avatar_default.png)
Currently seqlocks and seqcounts don't support lockdep. After running across a seqcount related deadlock in the timekeeping code, I used a less-refined and more focused variant of this patch to narrow down the cause of the issue. This is a first-pass attempt to properly enable lockdep functionality on seqlocks and seqcounts. Since seqcounts are used in the vdso gettimeofday code, I've provided non-lockdep accessors for those needs. I've also handled one case where there were nested seqlock writers and there may be more edge cases. Comments and feedback would be appreciated! Signed-off-by: John Stultz <john.stultz@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Li Zefan <lizefan@huawei.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: netdev@vger.kernel.org Link: http://lkml.kernel.org/r/1381186321-4906-3-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
395 lines
10 KiB
C
395 lines
10 KiB
C
#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;
|
|
}
|
|
|
|
/**
|
|
* 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
|
|
*
|
|
* 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 read_seqcount_begin_no_lockdep(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);
|
|
|
|
seqcount_lockdep_reader_access(s);
|
|
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);
|
|
}
|
|
|
|
|
|
/*
|
|
* Sequence counter only version assumes that callers are using their
|
|
* own mutexing.
|
|
*/
|
|
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++;
|
|
}
|
|
|
|
/**
|
|
* 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);
|
|
}
|
|
|
|
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 */
|