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SubjectRe: ntp: BUG: spinlock lockup on CPU#1
On Thu, 15 Mar 2012, Thomas Gleixner wrote:
> 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);
>
> So CPU0 waits for xtime seqence to become valid and CPU1 cant make
> progress because it's stuck on ntp_lock.

The same problem exists with ntp_clear() being called under the
xtime/timekeeper lock write locked. Nasty ...


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