On 2015/1/22 4:06, Paul E. McKenney wrote: > On Wed, Jan 21, 2015 at 10:10:51AM -0500, Don Zickus wrote: >> On Wed, Jan 21, 2015 at 10:26:27AM +0800, Zhang Zhen wrote: >>>> This may not cause other problems but what happens if you comment out the >>>> 'touch_softlockup_watchdog' from the touch_nmi_watchdog function like >>>> below (based on latest upstream cb59670870)? >>>> >>>> The idea is that console printing for that cpu won't reset the softlockup >>>> detector. Again other bad things might happen and this patch may not be a >>>> good final solution, but it can help give me a clue about what is going >>>> on. >>> >>> I commented out the 'touch_softlockup_watchdog' from the touch_nmi_watchdog >>> function >>> (based on latest upstream ec6f34e5b552). >>> This triggered RCU stall and softlockup, but softlockup just printk only >>> once. >> >> Yes, as expected. Instead of flooding the console with the same message, >> report only once until the high priority task is re-kicked and can re-arm >> the softlockup timer again. So this makes sense. Based on your double >> spin lock test, I don't ever expect this to get re-armed, so you should >> not expect to see another message. >> >> >>> As you mentioned "other bad things" lead to softlockup just printk only >>> once. >>> What's the bad thing ? >> >> Well, one of the assumptions here is that if you are going to have >> interrupts disabled for a long time and purposely kick the hardlockup >> detector (with touch_nmi_watchdog), then you can reasonably assume that >> softlockups will go off too if you don't also kick the softlockup detector >> (even though there is a window where this isn't true: 2*thresh - thresh). >> >> >> So the patch I gave you, can lead to false softlockup warnings. >> >> >> On the flip side, printing to the console also blocks hardlockups from >> showing up. But I believe loooong ago, Paul adjusted the rcu stalls to be >> longer than a hardlockup/softlockup timeout to prevent such scenarios. >> >> >> >> I am not sure what to do here. Printing to the console has traditionally >> been slow (especially if doing so with interrupts disabled), so a >> touch_nmi_watchdog has been necessary. But a side effect of that, is it >> prevents the lockup detectors from going off if printing repeatedly. >> >> >> Now we can hack up rcu stall to only print once until it is re-armed. >> This would show rcu stall printing first, followed two minutes later by >> a softlockup, which sorta achieves what you want. >> >> >> >> However, at the end of the day, an rcu stall, softlockup or hardlockup is >> a bad thing, does it matter if you get one or all of them? One should be >> enough to start an investigation, no? > > Hear, hear!!! > Ok, thanks for Don's and your patience! We enriched softlockup printk information, so we want to get softlockup warnning.
> Thanx, Paul > >> I don't know. I am leaning towards 'working as expected' and nothing to >> really fix here. Does anyone have any suggestions on what assumptions we >> could change to handle this better? >> >> >> Cheers, >> Don >> >>> >>> / # >>> / # echo 60 > /proc/sys/kernel/watchdog_thresh >>> / # busybox insmod softlockup_test.ko & >>> / # [ 39.044058] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=21002 jiffies, g=78, c=77, q=4) >>> [ 39.044058] INFO: Stall ended before state dump start >>> [ 102.049045] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=84007 jiffies, g=78, c=77, q=4) >>> [ 102.049045] INFO: Stall ended before state dump start >>> [ 160.482123] BUG: soft lockup - CPU#0 stuck for 134s! [busybox:54] >>> [ 165.054075] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=147012 jiffies, g=78, c=77, q=4) >>> [ 165.054075] INFO: Stall ended before state dump start >>> [ 228.059045] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=210017 jiffies, g=78, c=77, q=4) >>> [ 228.059045] INFO: Stall ended before state dump start >>> [ 291.064099] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=273022 jiffies, g=78, c=77, q=4) >>> [ 291.064099] INFO: Stall ended before state dump start >>> [ 354.069074] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=336027 jiffies, g=78, c=77, q=4) >>> [ 354.069099] INFO: Stall ended before state dump start >>> [ 417.074045] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=399032 jiffies, g=78, c=77, q=4) >>> [ 417.074045] INFO: Stall ended before state dump start >>> [ 480.079099] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=462037 jiffies, g=78, c=77, q=4) >>> [ 480.079099] INFO: Stall ended before state dump start >>> [ 543.084099] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=525042 jiffies, g=78, c=77, q=4) >>> [ 543.084099] INFO: Stall ended before state dump start >>> [ 606.089101] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=588047 jiffies, g=78, c=77, q=4) >>> [ 606.089101] INFO: Stall ended before state dump start >>> [ 669.094099] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=651052 jiffies, g=78, c=77, q=4) >>> [ 669.094099] INFO: Stall ended before state dump start >>> [ 732.099045] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=714057 jiffies, g=78, c=77, q=4) >>> [ 732.099045] INFO: Stall ended before state dump start >>> [ 795.104074] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=777062 jiffies, g=78, c=77, q=4) >>> [ 795.104098] INFO: Stall ended before state dump start >>> [ 858.109046] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=840067 jiffies, g=78, c=77, q=4) >>> [ 858.109046] INFO: Stall ended before state dump start >>> [ 921.114100] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=903072 jiffies, g=78, c=77, q=4) >>> [ 921.114100] INFO: Stall ended before state dump start >>> [ 984.119099] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=966077 jiffies, g=78, c=77, q=4) >>> [ 984.119099] INFO: Stall ended before state dump start >>> [ 1047.124075] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1029082 jiffies, g=78, c=77, q=4) >>> [ 1047.124099] INFO: Stall ended before state dump start >>> [ 1110.129046] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1092087 jiffies, g=78, c=77, q=4) >>> [ 1110.129046] INFO: Stall ended before state dump start >>> [ 1173.134045] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1155092 jiffies, g=78, c=77, q=4) >>> [ 1173.134045] INFO: Stall ended before state dump start >>> [ 1236.139101] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1218097 jiffies, g=78, c=77, q=4) >>> [ 1236.139101] INFO: Stall ended before state dump start >>> [ 1299.144059] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1281102 jiffies, g=78, c=77, q=4) >>> [ 1299.144059] INFO: Stall ended before state dump start >>> [ 1362.149099] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1344107 jiffies, g=78, c=77, q=4) >>> [ 1362.149099] INFO: Stall ended before state dump start >>> [ 1425.154059] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1407112 jiffies, g=78, c=77, q=4) >>> [ 1425.154059] INFO: Stall ended before state dump start >>> [ 1488.159046] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1470117 jiffies, g=78, c=77, q=4) >>> [ 1488.159046] INFO: Stall ended before state dump start >>> [ 1551.164045] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1533122 jiffies, g=78, c=77, q=4) >>> [ 1551.164045] INFO: Stall ended before state dump start >>> [ 1614.169057] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1596127 jiffies, g=78, c=77, q=4) >>> [ 1614.169057] INFO: Stall ended before state dump start >>> [ 1677.174060] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1659132 jiffies, g=78, c=77, q=4) >>> [ 1677.174060] INFO: Stall ended before state dump start >>> [ 1740.179045] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1722137 jiffies, g=78, c=77, q=4) >>> [ 1740.179045] INFO: Stall ended before state dump start >>> [ 1803.184075] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1785142 jiffies, g=78, c=77, q=4) >>> [ 1803.184101] INFO: Stall ended before state dump start >>> [ 1866.189046] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1848147 jiffies, g=78, c=77, q=4) >>> [ 1866.189046] INFO: Stall ended before state dump start >>> [ 1929.194045] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1911152 jiffies, g=78, c=77, q=4) >>> [ 1929.194045] INFO: Stall ended before state dump start >>> [ 1992.199083] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=1974157 jiffies, g=78, c=77, q=4) >>> [ 1992.199083] INFO: Stall ended before state dump start >>> [ 2055.204098] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=2037162 jiffies, g=78, c=77, q=4) >>> [ 2055.204098] INFO: Stall ended before state dump start >>> [ 2118.209045] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=2100167 jiffies, g=78, c=77, q=4) >>> [ 2118.209045] INFO: Stall ended before state dump start >>> [ 2181.214098] INFO: rcu_preempt detected stalls on CPUs/tasks: {} >>> (detected by 0, t=2163172 jiffies, g=78, c=77, q=4) >>> [ 2181.214098] INFO: Stall ended before state dump start >>>> >>>> Cheers, >>>> Don >>>> >>>> diff --git a/kernel/watchdog.c b/kernel/watchdog.c >>>> index 70bf118..833c015 100644 >>>> --- a/kernel/watchdog.c >>>> +++ b/kernel/watchdog.c >>>> @@ -209,7 +209,7 @@ void touch_nmi_watchdog(void) >>>> * going off. >>>> */ >>>> raw_cpu_write(watchdog_nmi_touch, true); >>>> - touch_softlockup_watchdog(); >>>> + //touch_softlockup_watchdog(); >>>> } >>>> EXPORT_SYMBOL(touch_nmi_watchdog); >>>> >>>> >>>> . >>>> >>> >>> >> > > > . > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/