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Subject[PATCH 02/26] seqlock: Create raw_seqlock
Date
From: Thomas Gleixner <tglx@linutronix.de>

raw_seqlock_t will be used to annotate seqlocks which can not be
converted to sleeping locks in preempt-rt

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

The original patch 09e46c7a86b2e81f97bd93f588b62c2d36cff58e used atomic_locks
I converted this patch to raw_locks.

Signed-off-by: John Kacur <jkacur@redhat.com>
---
include/linux/seqlock.h | 86 ++++++++++++++++++++++++++++++++++++++++++++--
1 files changed, 82 insertions(+), 4 deletions(-)

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 632205c..6f2685c 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -31,6 +31,11 @@

typedef struct {
unsigned sequence;
+ raw_spinlock_t lock;
+} raw_seqlock_t;
+
+typedef struct {
+ unsigned sequence;
spinlock_t lock;
} seqlock_t;

@@ -38,11 +43,23 @@ typedef struct {
* These macros triggered gcc-3.x compile-time problems. We think these are
* OK now. Be cautious.
*/
+#define __RAW_SEQLOCK_UNLOCKED(lockname) \
+ { 0, __RAW_SPIN_LOCK_UNLOCKED(lockname) }
+
+#define seqlock_raw_init(x) \
+ do { \
+ (x)->sequence = 0; \
+ raw_spin_lock_init(&(x)->lock); \
+ } while (0)
+
+#define DEFINE_RAW_SEQLOCK(x) \
+ raw_seqlock_t x = __RAW_SEQLOCK_UNLOCKED(x)
+
#define __SEQLOCK_UNLOCKED(lockname) \
- { 0, __SPIN_LOCK_UNLOCKED(lockname) }
+ { 0, __SPIN_LOCK_UNLOCKED(lockname) }

#define SEQLOCK_UNLOCKED \
- __SEQLOCK_UNLOCKED(old_style_seqlock_init)
+ __SEQLOCK_UNLOCKED(old_style_seqlock_init)

#define seqlock_init(x) \
do { \
@@ -51,12 +68,19 @@ typedef struct {
} while (0)

#define DEFINE_SEQLOCK(x) \
- seqlock_t x = __SEQLOCK_UNLOCKED(x)
+ seqlock_t x = __SEQLOCK_UNLOCKED(x)

/* 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_raw_seqlock(raw_seqlock_t *sl)
+{
+ raw_spin_lock(&sl->lock);
+ ++sl->sequence;
+ smp_wmb();
+}
+
static inline void write_seqlock(seqlock_t *sl)
{
spin_lock(&sl->lock);
@@ -64,6 +88,13 @@ static inline void write_seqlock(seqlock_t *sl)
smp_wmb();
}

+static inline void write_raw_sequnlock(raw_seqlock_t *sl)
+{
+ smp_wmb();
+ sl->sequence++;
+ raw_spin_unlock(&sl->lock);
+}
+
static inline void write_sequnlock(seqlock_t *sl)
{
smp_wmb();
@@ -83,6 +114,21 @@ static inline int write_tryseqlock(seqlock_t *sl)
}

/* Start of read calculation -- fetch last complete writer token */
+static __always_inline unsigned read_raw_seqbegin(const raw_seqlock_t *sl)
+{
+ unsigned ret;
+
+repeat:
+ ret = sl->sequence;
+ smp_rmb();
+ if (unlikely(ret & 1)) {
+ cpu_relax();
+ goto repeat;
+ }
+
+ return ret;
+}
+
static __always_inline unsigned read_seqbegin(const seqlock_t *sl)
{
unsigned ret;
@@ -103,6 +149,14 @@ repeat:
*
* If sequence value changed then writer changed data while in section.
*/
+static __always_inline int
+read_raw_seqretry(const raw_seqlock_t *sl, unsigned start)
+{
+ smp_rmb();
+
+ return (sl->sequence != start);
+}
+
static __always_inline int read_seqretry(const seqlock_t *sl, unsigned start)
{
smp_rmb();
@@ -170,12 +224,36 @@ static inline void write_seqcount_end(seqcount_t *s)
/*
* Possible sw/hw IRQ protected versions of the interfaces.
*/
+#define write_raw_seqlock_irqsave(lock, flags) \
+ do { local_irq_save(flags); write_raw_seqlock(lock); } while (0)
+#define write_raw_seqlock_irq(lock) \
+ do { local_irq_disable(); write_raw_seqlock(lock); } while (0)
+#define write_raw_seqlock_bh(lock) \
+ do { local_bh_disable(); write_raw_seqlock(lock); } while (0)
+
+#define write_raw_sequnlock_irqrestore(lock, flags) \
+ do { write_raw_sequnlock(lock); local_irq_restore(flags); } while(0)
+#define write_raw_sequnlock_irq(lock) \
+ do { write_raw_sequnlock(lock); local_irq_enable(); } while(0)
+#define write_raw_sequnlock_bh(lock) \
+ do { write_raw_sequnlock(lock); local_bh_enable(); } while(0)
+
+#define read_raw_seqbegin_irqsave(lock, flags) \
+ ({ local_irq_save(flags); read_raw_seqbegin(lock); })
+
+#define read_raw_seqretry_irqrestore(lock, iv, flags) \
+ ({ \
+ int ret = read_raw_seqretry(lock, iv); \
+ local_irq_restore(flags); \
+ ret; \
+ })
+
#define write_seqlock_irqsave(lock, flags) \
do { local_irq_save(flags); write_seqlock(lock); } while (0)
#define write_seqlock_irq(lock) \
do { local_irq_disable(); write_seqlock(lock); } while (0)
#define write_seqlock_bh(lock) \
- do { local_bh_disable(); write_seqlock(lock); } while (0)
+ do { local_bh_disable(); write_seqlock(lock); } while (0)

#define write_sequnlock_irqrestore(lock, flags) \
do { write_sequnlock(lock); local_irq_restore(flags); } while(0)
--
1.6.5.2


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