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Message-ID: <20080422091456.GC9939@elte.hu> Date: Tue, 22 Apr 2008 11:14:56 +0200 From: Ingo Molnar <mingo@...e.hu> To: David Miller <davem@...emloft.net> Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de> Subject: Re: Soft lockup regression from today's sched.git merge. * David Miller <davem@...emloft.net> wrote: > The following commit: > > commit 27ec4407790d075c325e1f4da0a19c56953cce23 > Author: Ingo Molnar <mingo@...e.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@...e.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 yeah, it looks very similar. > Please have a look, thank you. thanks for reporting it. I havent seen this false positive happen in a long time - but then again, PC CPUs are a lot less idle than a 128-CPU Niagara2 :-/ I'm wondering what the best method would be to provoke a CPU to stay idle that long - to make sure this bug is fixed. so i only have the untested patch below for now - does it fix the bug for you? Ingo -----------------------------------> Subject: softlockup: fix NOHZ wakeup From: Ingo Molnar <mingo@...e.hu> David Miller reported: |---------------> the following commit: | commit 27ec4407790d075c325e1f4da0a19c56953cce23 | Author: Ingo Molnar <mingo@...e.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@...e.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: Ingo Molnar <mingo@...e.hu> --- kernel/time/tick-sched.c | 1 + 1 file changed, 1 insertion(+) Index: linux/kernel/time/tick-sched.c =================================================================== --- linux.orig/kernel/time/tick-sched.c +++ linux/kernel/time/tick-sched.c @@ -393,6 +393,7 @@ void tick_nohz_restart_sched_tick(void) sub_preempt_count(HARDIRQ_OFFSET); } + touch_softlockup_watchdog(); /* * Cancel the scheduled timer and restore the tick */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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