Use the shadow timekeeper to do the update_wall_time() adjustments and
then copy it over to the real timekeeper.
Keep the shadow timekeeper in sync when updating stuff outside of
update_wall_time().
This allows us to limit the timekeeper_seq hold time to the update of
the real timekeeper and the vsyscall data in the next patch.
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
---
kernel/time/timekeeping.c | 41 +++++++++++++++++++++++++++++------------
1 file changed, 29 insertions(+), 12 deletions(-)
Index: linux-3.6/kernel/time/timekeeping.c
===================================================================
--- linux-3.6.orig/kernel/time/timekeeping.c
+++ linux-3.6/kernel/time/timekeeping.c
@@ -28,6 +28,7 @@
static struct timekeeper timekeeper;
static DEFINE_RAW_SPINLOCK(timekeeper_lock);
static seqcount_t timekeeper_seq;
+static struct timekeeper shadow_timekeeper;
/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;
@@ -224,7 +225,7 @@ int pvclock_gtod_unregister_notifier(str
EXPORT_SYMBOL_GPL(pvclock_gtod_unregister_notifier);
/* must hold timekeeper_lock */
-static void timekeeping_update(struct timekeeper *tk, bool clearntp)
+static void timekeeping_update(struct timekeeper *tk, bool clearntp, bool
mirror)
{
if (clearntp) {
tk->ntp_error = 0;
@@ -232,6 +233,9 @@ static void timekeeping_update(struct ti
}
update_vsyscall(tk);
update_pvclock_gtod(tk);
+
+ if (mirror)
+ memcpy(&shadow_timekeeper, &timekeeper, sizeof(timekeeper));
}
/**
@@ -444,7 +448,7 @@ int do_settimeofday(const struct timespe
tk_set_xtime(tk, tv);
- timekeeping_update(tk, true);
+ timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@@ -488,7 +492,7 @@ int timekeeping_inject_offset(struct tim
tk_set_wall_to_mono(tk, timespec_sub(tk->wall_to_monotonic, *ts));
error: /* even if we error out, we forwarded the time, so call update */
- timekeeping_update(tk, true);
+ timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@@ -523,7 +527,7 @@ static int change_clocksource(void *data
if (old->disable)
old->disable(old);
}
- timekeeping_update(tk, true);
+ timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@@ -704,6 +708,8 @@ void __init timekeeping_init(void)
tmp.tv_nsec = 0;
tk_set_sleep_time(tk, tmp);
+ memcpy(&shadow_timekeeper, &timekeeper, sizeof(timekeeper));
+
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
}
@@ -760,7 +766,7 @@ void timekeeping_inject_sleeptime(struct
__timekeeping_inject_sleeptime(tk, delta);
- timekeeping_update(tk, true);
+ timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@@ -798,7 +804,7 @@ static void timekeeping_resume(void)
tk->clock->cycle_last = tk->clock->read(tk->clock);
tk->ntp_error = 0;
timekeeping_suspended = 0;
- timekeeping_update(tk, false);
+ timekeeping_update(tk, false, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@@ -1177,7 +1183,8 @@ static inline void old_vsyscall_fixup(st
static void update_wall_time(void)
{
struct clocksource *clock;
- struct timekeeper *tk = &timekeeper;
+ struct timekeeper *real_tk = &timekeeper;
+ struct timekeeper *tk = &shadow_timekeeper;
cycle_t offset;
int shift = 0, maxshift;
unsigned long flags;
@@ -1189,16 +1196,16 @@ static void update_wall_time(void)
if (unlikely(timekeeping_suspended))
goto out;
- clock = tk->clock;
+ clock = real_tk->clock;
#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
- offset = tk->cycle_interval;
+ offset = real_tk->cycle_interval;
#else
offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
#endif
/* Check if there's really nothing to do */
- if (offset < tk->cycle_interval)
+ if (offset < real_tk->cycle_interval)
goto out;
/*
@@ -1237,12 +1244,22 @@ static void update_wall_time(void)
/* Update clock->cycle_last with the new value */
clock->cycle_last = tk->cycle_last;
- timekeeping_update(tk, false);
+ /*
+ * Update the real timekeeper.
+ *
+ * We could avoid this memcpy by switching pointers, but that
+ * requires changes to all other timekeeper usage sites as
+ * well, i.e. move the timekeeper pointer getter into the
+ * spinlocked/seqcount protected sections. And we trade this
+ * memcpy under the timekeeper_seq against one before we start
+ * updating.
+ */
+ memcpy(real_tk, tk, sizeof(*tk));
+ timekeeping_update(real_tk, false, false);
out:
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
-
}
/**
--
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