Messages in this thread | | | Date | Sun, 01 Jul 2012 14:00:28 +0200 | From | Jan Ceuleers <> | Subject | Re: [PATCH] [RFC] Potential fix for leapsecond caused futex related load spikes |
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On 07/01/2012 11:36 AM, John Stultz wrote: > I believe this issue is due to the leapsecond being added without > calling clock_was_set() to notify the hrtimer subsystem of the > change. (Although I've not yet chased all the way down to the > hrtimer code to validate exactly what's going on there).
For the benefit of -stable:
Am I right in thinking that, if the analysis is confirmed, this was caused by the following commit:
commit 746976a301ac9c9aa10d7d42454f8d6cdad8ff2b Author: Thomas Gleixner <tglx@linutronix.de> Date: Tue Jul 3 20:05:20 2007 +0200
NTP: remove clock_was_set() call to prevent deadlock
The clock_was_set() call in seconds_overflow() which happens only when leap seconds are inserted / deleted is wrong in two aspects:
1. it results in a call to on_each_cpu() with interrupts disabled 2. it is potential deadlock source vs. call_lock in smp_call_function()
The only possible side effect of the removal might be, that an absolute CLOCK_REALTIME timer fires 1 second too late, in the rare case of leap second deletion and an absolute CLOCK_REALTIME timer which expires in the affected time frame. It will never fire too early.
This was probably observed by the reporter of a June 30th -> July 1st hang: http://lkml.org/lkml/2007/7/3/103
A similar problem was observed by Dave Jones, who provided a screen shot with a lockdep back trace, which allowed to analyse the problem.
Sob: Thomas Gleixner <tglx@linutronix.de> Ab: Ingo Molnar <mingo@elte.hu> Sob: Linus Torvalds <torvalds@linux-foundation.org>
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