John Stultz 6b43ae8a61 ntp: Fix leap-second hrtimer livelock ... Since commit 7dffa3c673 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>		2012-03-22 19:43:43 -07:00
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time	ntp: Fix leap-second hrtimer livelock	2012-03-22 19:43:43 -07:00
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time.c	time: Remove bogus comments	2012-03-15 18:17:55 -07:00
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