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authorJohn Stultz <john.stultz@linaro.org>2012-03-16 00:04:03 +0400
committerJohn Stultz <john.stultz@linaro.org>2012-03-23 06:43:43 +0400
commit6b43ae8a619d17c4935c3320d2ef9e92bdeed05d (patch)
tree007df06a9cf0d4d2b72ed7dd8d646e853de80e9b /include/linux/timex.h
parent57779dc2b3b75bee05ef5d1ada47f615f7a13932 (diff)
downloadlinux-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 'include/linux/timex.h')
-rw-r--r--include/linux/timex.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/timex.h b/include/linux/timex.h
index b75e1864ed19..99bc88b1fc02 100644
--- a/include/linux/timex.h
+++ b/include/linux/timex.h
@@ -252,7 +252,7 @@ extern void ntp_clear(void);
/* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
extern u64 ntp_tick_length(void);
-extern void second_overflow(void);
+extern int second_overflow(unsigned long secs);
extern int do_adjtimex(struct timex *);
extern void hardpps(const struct timespec *, const struct timespec *);