timekeeping: Split timekeeper_lock into lock and seqcount

We want to shorten the seqcount write hold time. So split the seqlock
into a lock and a seqcount.

Open code the seqwrite_lock in the places which matter and drop the
sequence counter update where it's pointless.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[jstultz: Merge fixups from CLOCK_TAI collisions]
Signed-off-by: John Stultz <john.stultz@linaro.org>

1 files changed, 73 insertions, 59 deletions

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index caede71c0a35..5e048e030c62 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -26,7 +26,8 @@
 #include "tick-internal.h"
 
 static struct timekeeper timekeeper;
-static DEFINE_SEQLOCK(timekeeper_lock);
+static DEFINE_RAW_SPINLOCK(timekeeper_lock);
+static seqcount_t timekeeper_seq;
 
 /* flag for if timekeeping is suspended */
 int __read_mostly timekeeping_suspended;
@@ -204,8 +205,6 @@ static void update_pvclock_gtod(struct timekeeper *tk)
 
 /**
  * pvclock_gtod_register_notifier - register a pvclock timedata update listener
- *
- * Must hold write on timekeeper.lock
  */
 int pvclock_gtod_register_notifier(struct notifier_block *nb)
 {
@@ -213,11 +212,10 @@ int pvclock_gtod_register_notifier(struct notifier_block *nb)
         unsigned long flags;
         int ret;
 
-        write_seqlock_irqsave(&timekeeper_lock, flags);
+        raw_spin_lock_irqsave(&timekeeper_lock, flags);
         ret = raw_notifier_chain_register(&pvclock_gtod_chain, nb);
-        /* update timekeeping data */
         update_pvclock_gtod(tk);
-        write_sequnlock_irqrestore(&timekeeper_lock, flags);
+        raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
         return ret;
 }
@@ -226,23 +224,21 @@ EXPORT_SYMBOL_GPL(pvclock_gtod_register_notifier);
 /**
  * pvclock_gtod_unregister_notifier - unregister a pvclock
  * timedata update listener
- *
- * Must hold write on timekeeper.lock
  */
 int pvclock_gtod_unregister_notifier(struct notifier_block *nb)
 {
         unsigned long flags;
         int ret;
 
-        write_seqlock_irqsave(&timekeeper_lock, flags);
+        raw_spin_lock_irqsave(&timekeeper_lock, flags);
         ret = raw_notifier_chain_unregister(&pvclock_gtod_chain, nb);
-        write_sequnlock_irqrestore(&timekeeper_lock, flags);
+        raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
         return ret;
 }
 EXPORT_SYMBOL_GPL(pvclock_gtod_unregister_notifier);
 
-/* must hold write on timekeeper.lock */
+/* must hold timekeeper_lock */
 static void timekeeping_update(struct timekeeper *tk, bool clearntp)
 {
         if (clearntp) {
@@ -296,12 +292,12 @@ int __getnstimeofday(struct timespec *ts)
         s64 nsecs = 0;
 
         do {
-                seq = read_seqbegin(&timekeeper_lock);
+                seq = read_seqcount_begin(&timekeeper_seq);
 
                 ts->tv_sec = tk->xtime_sec;
                 nsecs = timekeeping_get_ns(tk);
 
-        } while (read_seqretry(&timekeeper_lock, seq));
+        } while (read_seqcount_retry(&timekeeper_seq, seq));
 
         ts->tv_nsec = 0;
         timespec_add_ns(ts, nsecs);
@@ -337,11 +333,11 @@ ktime_t ktime_get(void)
         WARN_ON(timekeeping_suspended);
 
         do {
-                seq = read_seqbegin(&timekeeper_lock);
+                seq = read_seqcount_begin(&timekeeper_seq);
                 secs = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
                 nsecs = timekeeping_get_ns(tk) + tk->wall_to_monotonic.tv_nsec;
 
-        } while (read_seqretry(&timekeeper_lock, seq));
+        } while (read_seqcount_retry(&timekeeper_seq, seq));
         /*
          * Use ktime_set/ktime_add_ns to create a proper ktime on
          * 32-bit architectures without CONFIG_KTIME_SCALAR.
@@ -368,12 +364,12 @@ void ktime_get_ts(struct timespec *ts)
         WARN_ON(timekeeping_suspended);
 
         do {
-                seq = read_seqbegin(&timekeeper_lock);
+                seq = read_seqcount_begin(&timekeeper_seq);
                 ts->tv_sec = tk->xtime_sec;
                 nsec = timekeeping_get_ns(tk);
                 tomono = tk->wall_to_monotonic;
 
-        } while (read_seqretry(&timekeeper_lock, seq));
+        } while (read_seqcount_retry(&timekeeper_seq, seq));
 
         ts->tv_sec += tomono.tv_sec;
         ts->tv_nsec = 0;
@@ -397,12 +393,12 @@ void timekeeping_clocktai(struct timespec *ts)
         WARN_ON(timekeeping_suspended);
 
         do {
-                seq = read_seqbegin(&timekeeper_lock);
+                seq = read_seqcount_begin(&timekeeper_seq);
 
                 ts->tv_sec = tk->xtime_sec + tk->tai_offset;
                 nsecs = timekeeping_get_ns(tk);
 
-        } while (read_seqretry(&timekeeper_lock, seq));
+        } while (read_seqcount_retry(&timekeeper_seq, seq));
 
         ts->tv_nsec = 0;
         timespec_add_ns(ts, nsecs);
@@ -445,7 +441,7 @@ void getnstime_raw_and_real(struct timespec *ts_raw, struct timespec *ts_real)
         WARN_ON_ONCE(timekeeping_suspended);
 
         do {
-                seq = read_seqbegin(&timekeeper_lock);
+                seq = read_seqcount_begin(&timekeeper_seq);
 
                 *ts_raw = tk->raw_time;
                 ts_real->tv_sec = tk->xtime_sec;
@@ -454,7 +450,7 @@ void getnstime_raw_and_real(struct timespec *ts_raw, struct timespec *ts_real)
                 nsecs_raw = timekeeping_get_ns_raw(tk);
                 nsecs_real = timekeeping_get_ns(tk);
 
-        } while (read_seqretry(&timekeeper_lock, seq));
+        } while (read_seqcount_retry(&timekeeper_seq, seq));
 
         timespec_add_ns(ts_raw, nsecs_raw);
         timespec_add_ns(ts_real, nsecs_real);
@@ -494,7 +490,8 @@ int do_settimeofday(const struct timespec *tv)
         if (!timespec_valid_strict(tv))
                 return -EINVAL;
 
-        write_seqlock_irqsave(&timekeeper_lock, flags);
+        raw_spin_lock_irqsave(&timekeeper_lock, flags);
+        write_seqcount_begin(&timekeeper_seq);
 
         timekeeping_forward_now(tk);
 
@@ -508,7 +505,8 @@ int do_settimeofday(const struct timespec *tv)
 
         timekeeping_update(tk, true);