Re: [PATCH] fix get_jiffies_64 to work on voyager

[James Bottomley <James.Bottomley@steeleye.com>]

On Tue, 2004-01-06 at 11:05, Andrew Morton wrote:
> No, it was much simpler in my case: log_buf_len_setup() was accidentally
> enabling interrupts early in boot and we were taking a timer interrupt
> while holding a write lock on xtime_lock.  sched_clock() was requiring a
> read lock and boom.

Voyager has no APIC local timer equivalent, so I rebroadcast the timer
tick to all CPUs.  However, the local tick is done in this thread with
the xtime_lock held as write and it can trigger the scheduler load
balancing, which needs to call sched_clock()....boom.

All in all, this does show that the xtime sequence lock is a bit too
fragile.  It also seems to show that we should redo the subarch timer
hooks if we want to make the sequence locks work.

I think there should be two hooks: one called holding the xtime write
lock for doing clock adjustment specific things and the other called
after we've released the xtime write lock.

James