From: John Stultz Date: Thu, 15 Mar 2012 20:04:03 +0000 (-0700) Subject: ntp: Fix leap-second hrtimer livelock X-Git-Tag: v3.4-rc1~44^2~9 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6b43ae8a619d17c4935c3320d2ef9e92bdeed05d;p=pandora-kernel.git 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 CC: Thomas Gleixner Reported-by: Sasha Levin Diagnoised-by: Thomas Gleixner Tested-by: Sasha Levin Signed-off-by: John Stultz --- Reading git-diff-tree failed