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seqcount: Add lockdep functionality to seqcount/seqlock structures

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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>
This commit is contained in:
John Stultz
2013-10-07 15:51:59 -07:00
committed by Ingo Molnar
parent 827da44c61
commit 1ca7d67cf5
7 changed files with 90 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/linux/seqlock.h
+72 -7
View File
@@ -34,6 +34,7 @@
#include <linux/spinlock.h>
#include <linux/preempt.h>
#include <linux/lockdep.h>
#include <asm/processor.h>
/*
@@ -44,10 +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)
@@ -75,6 +116,22 @@ 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
@@ -86,9 +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);
}
/**
@@ -108,6 +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;
}
@@ -152,14 +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++;
}
@@ -188,7 +253,7 @@ typedef struct {
*/
#define __SEQLOCK_UNLOCKED(lockname) \
{ \
.seqcount = SEQCNT_ZERO, \
.seqcount = SEQCNT_ZERO(lockname), \
.lock = __SPIN_LOCK_UNLOCKED(lockname) \
}