Re: [PATCH 00/11] 3.0-stable: Fix for leapsecond deadlock & hrtimer/futex issue

From: Willy Tarreau
Date: Tue Jul 17 2012 - 13:58:10 EST

Hi John,

On Tue, Jul 17, 2012 at 01:33:47PM -0400, John Stultz wrote:
> Here is backport of the leapsecond fixes to 3.0-stable. These are less
> straight forward, and should get closer review.
> This patch set addresses two issues:
> 1) Deadlock leapsecond issue that a few reports described.
> I spent some time over the weekend trying to find a way to reproduce
> the hard-hang issue some folks were reporting after the leapsecond.
> Initially I didn't think the 6b43ae8a619d17 leap-second hrimter livelock
> patch needed to be backported since, I assumed it required the ntp_lock
> split for it to be triggered, but looking again I found that the same
> issue could occur prior to splitting out the ntp_lock. So I've backported
> that fix (and its follow-on fixups) as well as created a test case
> to reproduce the hard-hang deadlock.
> 2) Early hrtimer/futex expiration issue that was more widely observed
> This is the load-spike issue that a number of folks saw that did not
> hard hang most boxes (although some reports did show nmi-watchdogs
> triggering due to sudden spinning in tight loops).
> I've booted and tested this entire patchset on two boxes and run through a
> number of leapsecond related stress tests. However, additional testing and
> review would be appreciated.
> The original commits backported in this set are:
> Deadlock issue fixes:
> ---------------------
> 6b43ae8a619d17c4935c3320d2ef9e92bdeed05d ntp: Fix leap-second hrtimer livelock
> dd48d708ff3e917f6d6b6c2b696c3f18c019feed ntp: Correct TAI offset during leap second
> fad0c66c4bb836d57a5f125ecd38bed653ca863a timekeeping: Fix CLOCK_MONOTONIC inconsistency during leapsecond
> Helper change: (allows the following fixes to backport more easily):
> --------------------------------------------------------------------
> cc06268c6a87db156af2daed6e96a936b955cc82 time: Move common updates to a function
> Hrtimer early-expiration issue fixes:
> -------------------------------
> f55a6faa384304c89cfef162768e88374d3312cb hrtimer: Provide clock_was_set_delayed()
> 4873fa070ae84a4115f0b3c9dfabc224f1bc7c51 timekeeping: Fix leapsecond triggered load spike issue
> 5b9fe759a678e05be4937ddf03d50e950207c1c0 timekeeping: Maintain ktime_t based offsets for hrtimers
> 196951e91262fccda81147d2bcf7fdab08668b40 hrtimers: Move lock held region in hrtimer_interrupt()
> f6c06abfb3972ad4914cef57d8348fcb2932bc3b timekeeping: Provide hrtimer update function
> 5baefd6d84163443215f4a99f6a20f054ef11236 hrtimer: Update hrtimer base offsets each hrtimer_interrupt
> 3e997130bd2e8c6f5aaa49d6e3161d4d29b43ab0 timekeeping: Add missing update call in timekeeping_resume()
> I've already done backports to all the stable kernels to 2.6.32, and
> will send out the rest soon.

That's very much appreciated, thank you! Do not hesitate to send me
your reproducers, I'll happily run some tests.

Best regards,

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