Re: [lkp] [rcu] a7410f28ce: INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 0-... } 25089 jiffies s: 9 root: 0x1/.

[Ye Xiaolong <xiaolong.ye@intel.com>]

On 11/28, Sebastian Andrzej Siewior wrote:
>On 2016-11-09 14:25:39 [+0800], kernel test robot wrote:
>> 
>> FYI, we noticed the following commit:
>> 
>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
>> commit a7410f28ceb566bda840b4afc278747c63383fb6 ("rcu: update: Make RCU_EXPEDITE_BOOT be the default")
>> 
>> in testcase: boot
>> 
>> on test machine: qemu-system-x86_64 -enable-kvm -cpu host -smp 2 -m 1G
>> 
>> caused below changes:
>> 
>> 
>> +-----------------------------------------------------------------------------------+------------+------------+
>> |                                                                                   | 9aa96e24ec | a7410f28ce |
>> +-----------------------------------------------------------------------------------+------------+------------+
>> | boot_successes                                                                    | 3          | 7          |
>> | boot_failures                                                                     | 17         | 17         |
>> | INFO:rcu_sched_self-detected_stall_on_CPU                                         | 17         | 14         |
>> | calltrace:mark_rodata_ro                                                          | 17         | 14         |
>> | INFO:rcu_sched_detected_stalls_on_CPUs/tasks                                      | 15         | 14         |
>> | INFO:rcu_sched_detected_expedited_stalls_on_CPUs/tasks:{#-...}#jiffies_s:#root:#/ | 0          | 15         |
>> +-----------------------------------------------------------------------------------+------------+------------+
>
>Is it correct to assume that there are RCU stalls with and without my
>patch but with my patch there are also "expedited" stalls?
>
>> [   38.504100] Write protecting the kernel read-only data: 47104k
>> [   38.511102] Freeing unused kernel memory: 720K (ffff88000314c000 - ffff880003200000)
>> [   38.547480] Freeing unused kernel memory: 1032K (ffff880003cfe000 - ffff880003e00000)
>> [  149.710631] INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 0-... } 25089 jiffies s: 9 root: 0x1/.
>> [  149.720353] blocking rcu_node structures:
>
>The other testing robot reported something similar against rcu/next.
>With my patch I get:
>
>[   14.260226] Freeing unused kernel memory: 536K (ffff88000277a000 - ffff880002800000)
>[   14.263114] Freeing unused kernel memory: 252K (ffff8800031c1000 - ffff880003200000)
>[   35.256735] INFO: rcu_sched self-detected stall on CPU
>[   35.257565]  1-...: (6299 ticks this GP) idle=0e2/140000000000001/0 softirq=90/90 fqs=2100 last_accelerate: 0000/c973, nonlazy_posted: 0, .D
>[   35.259410]   (t=6300 jiffies g=-252 c=-253 q=0)
>[   35.260106] Task dump for CPU 1:
>[   35.260608] swapper/0       R  running task        0     1      0 0x00000008
>[   35.261698]  ffff880036107cc0 ffffffff81181de2 0000000000021780 ffff880036121780
>[   35.262835]  0000000000000001 ffffffff832d7fc0 ffff880036107ce0 ffffffff8118616d
>[   35.263995]  ffffffff832d7fc0 0000000000000001 ffff880036107d30 ffffffff8128b3b8
>[   35.265131] Call Trace:
>[   35.265512]  <IRQ> [   35.265826]  [<ffffffff81181de2>] sched_show_task+0x102/0x180
>[   35.266701]  [<ffffffff8118616d>] dump_cpu_task+0x4d/0x60 
>[   35.267526]  [<ffffffff8128b3b8>] rcu_dump_cpu_stacks+0xee/0x11b
>…
>[   35.289870] INFO: rcu_sched detected stalls on CPUs/tasks:
>[   35.290500]  1-...: (6301 ticks this GP) idle=0e2/140000000000000/0 softirq=90/90 fqs=2100 last_accelerate: 0000/c97d, nonlazy_posted: 0, .D
>[   35.291834]  (detected by 0, t=6310 jiffies, g=-252, c=-253, q=0)
>[   35.292505] Task dump for CPU 1:
>…
>[   44.260103] INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 1-... } 6784 jiffies s: 299 root: 0x2/.
>[   44.261911] blocking rcu_node structures:
>[   44.262627] Task dump for CPU 1:
>[   44.263177] swapper/0       R  running task        0     1      0 0x00000008
>[   44.264379]  0000000041b58ab3 ffffffff81249eab ffffffff81b6f150 ffffffff819468d7
>[   44.265640]  0000000041b58ab3 ffffffff830f76b0 0000000000000297 ffffffff83d87aa0
>[   44.266915]  000000000000c6e0 0000000000000058 0000000000000000 ffff880035547be8
>[   44.268153] Call Trace:
>[   44.268603]  [<ffffffff81249eab>] ? trace_hardirqs_on_caller+0xdb/0x1e0
>[   44.269708]  [<ffffffff81b6f150>] ? serial8250_set_defaults+0x1a0/0x1a0
>
>and without it:
>[   15.837956] Freeing unused kernel memory: 536K (ffff88000277a000 - ffff880002800000)
>[   15.841396] Freeing unused kernel memory: 252K (ffff8800031c1000 - ffff880003200000)
>[   43.070453] INFO: rcu_sched self-detected stall on CPU
>[   43.071215]  1-...: (6299 ticks this GP) idle=daa/140000000000001/0 softirq=211/211 fqs=2100 last_accelerate: 0000/d29c, nonlazy_posted: 0, .D
>[   43.072807]   (t=6300 jiffies g=-91 c=-92 q=0)
>[   43.073385] Task dump for CPU 1:
>[   43.073800] swapper/0       R  running task        0     1      0 0x00000008
>[   43.074734]  ffff880036107cc0 ffffffff81181de2 0000000000021780 ffff880036121780
>[   43.075715]  0000000000000001 ffffffff832d7f80 ffff880036107ce0 ffffffff8118616d
>[   43.076691]  ffffffff832d7f80 0000000000000001 ffff880036107d30 ffffffff8128b3b8
>[   43.077668] Call Trace:
>[   43.077983]  <IRQ> [   43.078265]  [<ffffffff81181de2>] sched_show_task+0x102/0x180
>[   43.079006]  [<ffffffff8118616d>] dump_cpu_task+0x4d/0x60
>…
>[   43.097862] INFO: rcu_sched detected stalls on CPUs/tasks:
>[   43.098442]  1-...: (6300 ticks this GP) idle=daa/140000000000000/0 softirq=211/211 fqs=2100 last_accelerate: 0000/d2a4, nonlazy_posted: 0, .D
>[   43.099613]  (detected by 0, t=6308 jiffies, g=-91, c=-92, q=0)
>[   43.100180] Task dump for CPU 1:
>[   43.100487] swapper/0       R  running task        0     1      0 0x00000008
>[   43.101171]  ffffffff83d86c40 1ffff10006aa8f67 0000000500000058 0000000041b58ab3
>[   43.101912]  ffffffff8316ae78 ffffffff81b6f150 ffffffff819468d7 0000000041b58ab3
>[   43.102657]  ffffffff830f76b0 ffffffff81946830 ffff103000000020 ffff880000000020
>[   43.103395] Call Trace:
>[   43.103647]  [<ffffffff81b6f150>] ? serial8250_set_defaults+0x1a0/0x1a0
>[   43.104272]  [<ffffffff819468d7>] ? sprintf+0xa7/0xd0
>
>So it looks to me that the problem has been always there but the
>additional "expedited" part in the INFO message was the reason to create
>the report.

Thanks for the explanation, we'll ignore this kind of reports. And sorry for
the noise.

Thanks,
Xiaolong
>
>Sebastian