• Ingo Molnar's avatar
    softlockup: fix NOHZ wakeup · 126e01bf
    Ingo Molnar authored
    David Miller reported:
    
    |--------------->
    the following commit:
    
    | commit 27ec4407
    | Author: Ingo Molnar <mingo@elte.hu>
    | Date:   Thu Feb 28 21:00:21 2008 +0100
    |
    |     sched: make cpu_clock() globally synchronous
    |
    |     Alexey Zaytsev reported (and bisected) that the introduction of
    |     cpu_clock() in printk made the timestamps jump back and forth.
    |
    |     Make cpu_clock() more reliable while still keeping it fast when it's
    |     called frequently.
    |
    |     Signed-off-by: Ingo Molnar <mingo@elte.hu>
    
    causes watchdog triggers when a cpu exits NOHZ state when it has been
    there for >= the soft lockup threshold, for example here are some
    messages from a 128 cpu Niagara2 box:
    
    [  168.106406] BUG: soft lockup - CPU#11 stuck for 128s! [dd:3239]
    [  168.989592] BUG: soft lockup - CPU#21 stuck for 86s! [swapper:0]
    [  168.999587] BUG: soft lockup - CPU#29 stuck for 91s! [make:4511]
    [  168.999615] BUG: soft lockup - CPU#2 stuck for 85s! [swapper:0]
    [  169.020514] BUG: soft lockup - CPU#37 stuck for 91s! [swapper:0]
    [  169.020514] BUG: soft lockup - CPU#45 stuck for 91s! [sh:4515]
    [  169.020515] BUG: soft lockup - CPU#69 stuck for 92s! [swapper:0]
    [  169.020515] BUG: soft lockup - CPU#77 stuck for 92s! [swapper:0]
    [  169.020515] BUG: soft lockup - CPU#61 stuck for 92s! [swapper:0]
    [  169.112554] BUG: soft lockup - CPU#85 stuck for 92s! [swapper:0]
    [  169.112554] BUG: soft lockup - CPU#101 stuck for 92s! [swapper:0]
    [  169.112554] BUG: soft lockup - CPU#109 stuck for 92s! [swapper:0]
    [  169.112554] BUG: soft lockup - CPU#117 stuck for 92s! [swapper:0]
    [  169.171483] BUG: soft lockup - CPU#40 stuck for 80s! [dd:3239]
    [  169.331483] BUG: soft lockup - CPU#13 stuck for 86s! [swapper:0]
    [  169.351500] BUG: soft lockup - CPU#43 stuck for 101s! [dd:3239]
    [  169.531482] BUG: soft lockup - CPU#9 stuck for 129s! [mkdir:4565]
    [  169.595754] BUG: soft lockup - CPU#20 stuck for 93s! [swapper:0]
    [  169.626787] BUG: soft lockup - CPU#52 stuck for 93s! [swapper:0]
    [  169.626787] BUG: soft lockup - CPU#84 stuck for 92s! [swapper:0]
    [  169.636812] BUG: soft lockup - CPU#116 stuck for 94s! [swapper:0]
    
    It's simple enough to trigger this by doing a 10 minute sleep after a
    fresh bootup then starting a parallel kernel build.
    
    I suspect this might be reintroducing a problem we've had and fixed
    before, see the thread:
    
    http://marc.info/?l=linux-kernel&m=119546414004065&w=2
    <---------------|
    
    touch the softlockup watchdog when exiting NOHZ state - we are
    obviously not locked up.
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    126e01bf
tick-sched.c 17 KB