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author | John Stultz <john.stultz@linaro.org> | 2012-03-15 20:04:03 (GMT) |
---|---|---|
committer | John Stultz <john.stultz@linaro.org> | 2012-03-23 02:43:43 (GMT) |
commit | 6b43ae8a619d17c4935c3320d2ef9e92bdeed05d (patch) | |
tree | 007df06a9cf0d4d2b72ed7dd8d646e853de80e9b /kernel/time/timekeeping.c | |
parent | 57779dc2b3b75bee05ef5d1ada47f615f7a13932 (diff) | |
download | linux-fsl-qoriq-6b43ae8a619d17c4935c3320d2ef9e92bdeed05d.tar.xz |
ntp: Fix leap-second hrtimer livelock
Since commit 7dffa3c673fbcf835cd7be80bb4aec8ad3f51168 the ntp
subsystem has used an hrtimer for triggering the leapsecond
adjustment. However, this can cause a potential livelock.
Thomas diagnosed this as the following pattern:
CPU 0 CPU 1
do_adjtimex()
spin_lock_irq(&ntp_lock);
process_adjtimex_modes(); timer_interrupt()
process_adj_status(); do_timer()
ntp_start_leap_timer(); write_lock(&xtime_lock);
hrtimer_start(); update_wall_time();
hrtimer_reprogram(); ntp_tick_length()
tick_program_event() spin_lock(&ntp_lock);
clockevents_program_event()
ktime_get()
seq = req_seqbegin(xtime_lock);
This patch tries to avoid the problem by reverting back to not using
an hrtimer to inject leapseconds, and instead we handle the leapsecond
processing in the second_overflow() function.
The downside to this change is that on systems that support highres
timers, the leap second processing will occur on a HZ tick boundary,
(ie: ~1-10ms, depending on HZ) after the leap second instead of
possibly sooner (~34us in my tests w/ x86_64 lapic).
This patch applies on top of tip/timers/core.
CC: Sasha Levin <levinsasha928@gmail.com>
CC: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Sasha Levin <levinsasha928@gmail.com>
Diagnoised-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Diffstat (limited to 'kernel/time/timekeeping.c')
-rw-r--r-- | kernel/time/timekeeping.c | 20 |
1 files changed, 6 insertions, 14 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index b53da5e..5d76e09 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -184,18 +184,6 @@ static void timekeeping_update(bool clearntp) } -void timekeeping_leap_insert(int leapsecond) -{ - unsigned long flags; - - write_seqlock_irqsave(&timekeeper.lock, flags); - timekeeper.xtime.tv_sec += leapsecond; - timekeeper.wall_to_monotonic.tv_sec -= leapsecond; - timekeeping_update(false); - write_sequnlock_irqrestore(&timekeeper.lock, flags); - -} - /** * timekeeping_forward_now - update clock to the current time * @@ -969,9 +957,11 @@ static cycle_t logarithmic_accumulation(cycle_t offset, int shift) timekeeper.xtime_nsec += timekeeper.xtime_interval << shift; while (timekeeper.xtime_nsec >= nsecps) { + int leap; timekeeper.xtime_nsec -= nsecps; timekeeper.xtime.tv_sec++; - second_overflow(); + leap = second_overflow(timekeeper.xtime.tv_sec); + timekeeper.xtime.tv_sec += leap; } /* Accumulate raw time */ @@ -1082,9 +1072,11 @@ static void update_wall_time(void) * xtime.tv_nsec isn't larger then NSEC_PER_SEC */ if (unlikely(timekeeper.xtime.tv_nsec >= NSEC_PER_SEC)) { + int leap; timekeeper.xtime.tv_nsec -= NSEC_PER_SEC; timekeeper.xtime.tv_sec++; - second_overflow(); + leap = second_overflow(timekeeper.xtime.tv_sec); + timekeeper.xtime.tv_sec += leap; } timekeeping_update(false); |