Re: [PATCH 1/2] [RFC] Fix clock_was_set so it is safe to call fromatomic

From: John Stultz
Date: Mon Jul 02 2012 - 18:13:13 EST

On 07/02/2012 01:53 AM, Thomas Gleixner wrote:
On Sun, 1 Jul 2012, John Stultz wrote:

NOTE:This is a prerequisite patch that's required to
address the widely observed leap-second related futex/hrtimer

Currently clock_was_set() is unsafe to be called from atomic
context, as it calls on_each_cpu(). This causes problems when
we need to adjust the time from update_wall_time().

To fix this, introduce a work_struct so if we're in_atomic,
we can schedule work to do the necessary update after we're
out of the atomic section.
Shouldn't we queue a timer_list timer with expiry time jiffies + 0
instead. We can call on_each_cpu() from softirq context. And that
ensures that the update happens right away, while a scheduled work
might be delayed arbitrary long.
Thanks for the feedback.
I've implemented this, but before I send it out, I'm trying to see if there's not a way to change hrtimers so it doesn't keep its own per-cpu sense of time. If I don't sort that out shortly, I'll go ahead and send your suggestion out for inclusion so the fix is committed and I can try to further improve it afterwards.


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