Re: [printk] b031a684bf: INFO:rcu_tasks_detected_stalls_on_tasks

[Petr Mladek <pmladek@suse.com>]

On Thu 2021-01-28 16:48:29, John Ogness wrote:
> On 2021-01-28, Petr Mladek <pmladek@suse.com> wrote:
> > If you are able to reproduce this, it might be interesting to see
> > backtraces from all CPUs when RCU stall gets detected. Or even
> > printing all processes, even the sleeping ones.
> 
> OK, I now have lkp running on my intel core i5 machine and it reliably
> reproduces this. First let me say a word about lkp. The instructions in
> the report email are a bit misleading. There are lots of steps that it
> doesn't mention.
> 
> First I needed to install lkp and its dependencies. I did all of this as
> root because lkp seems to get confused when sudo is involved.
> 
> # git clone https://github.com/intel/lkp-tests.git
> # cd lkp-tests
> # make install
> # lkp install
> 
> Then I built the kernel and modules using a helper script to setup the
> environment for me:
> 
> ----- BEGIN /tmp/mk.sh -----
> #!/bin/sh
> 
> export INSTALL_MOD_PATH=`pwd`
> export HOSTCC=gcc-9
> export CC=gcc-9
> export ARCH=x86_64
> 
> exec make "$@"
> ----- END /tmp/mk.sh -----
> 
> # cd linux
> # git checkout -b lkp b031a684bfd01d633c79d281bd0cf11c2f834ada
> # cp /tmp/config-5.10.0-rc5-gb031a684bfd0 .config
> # /tmp/mk.sh -j `nproc` olddefconfig prepare modules_prepare bzImage modules modules_install
> 
> Then I created the modules.cgz:
> 
> # find lib/modules | cpio -H newc -o | gzip -9c > modules.cgz
> 
> I put kernel and modules in /tmp/:
> 
> # cp arch/x86/boot/bzImage modules.cgz /tmp/
> 
> And ran lkp inside script(1) so I have a logfile:
> 
> # script
> # lkp qemu -k /tmp/bzImage -m /tmp/modules.cgz /tmp/job-script
> 
> And reliably I see the first stall at about 925 seconds:
> 
> [  926.386441][   T22] INFO: rcu_tasks detected stalls on tasks:
> [  926.387310][   T22] 0000000041eb5240: .. nvcsw: 0/0 holdout: 1 idle_cpu: -1/1
> [  926.388196][   T22] task:dmesg           state:R  running task     stack:    0 pid: 1752 ppid:   511 flags:0x2002000
> 0
> [  926.389509][   T22] Call Trace:
> [  926.389962][   T22]  __schedule+0xa12/0xab5
> [  926.390534][   T22]  ? firmware_map_remove+0xd1/0xd1
> [  926.391190][   T22]  ? ksys_read+0x116/0x150
> [  926.391773][   T22]  schedule+0x16c/0x1df
> [  926.392317][   T22]  exit_to_user_mode_loop+0x28/0x84
> [  926.392977][   T22]  exit_to_user_mode_prepare+0x1d/0x4a
> [  926.393671][   T22]  syscall_exit_to_user_mode+0x41/0x4f
> [  926.394357][   T22]  entry_INT80_compat+0x71/0x76
> [  926.394982][   T22] RIP: 0023:0xf7f0fa02
> [  926.395528][   T22] RSP: 002b:00000000ff850364 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
> [  926.396590][   T22] RAX: ffffffffffffffe0 RBX: 0000000000000004 RCX: 00000000565c8234
> [  926.397607][   T22] RDX: 0000000000001fff RSI: 00000000000001e0 RDI: 00000000565c8234
> [  926.398617][   T22] RBP: 00000000ffffffff R08: 0000000000000000 R09: 0000000000000000
> [  926.399629][   T22] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> [  926.400643][   T22] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> 
> But actually it is not the rcu stall that interests me so much. I am
> more interested in some bizarre console output I am seeing. Here is a
> snippet:
> 
> [  903.008486][  T356] [  778.732883] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.008496][  T356]
> [  903.014733][  T528] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.030232][  T356] [  778.735197] [  655.203106] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.030242][  T356]
> [  903.040809][  T528] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.044327][  T356] [  778.746898] [  655.214214] [  531.584847] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.044337][  T356]
> [  903.048732][  T528] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.066039][  T356] [  778.751162] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.066050][  T356]
> [  903.070123][  T528] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.077137][  T356] [  778.768744] [  655.227204] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.077147][  T356]
> [  903.092792][  T528] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.095313][  T356] [  778.773836] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.095323][  T356]
> [  903.106788][  T356] [  778.781780] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.106798][  T356]
> [  903.121986][  T356] [  778.791183] [  655.230287] [  531.589973] [  407.116952] [  283.068815] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.121997][  T356]
> [  903.134120][  T356] [  778.797950] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.134130][  T356]
> [  903.148741][  T528] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.151626][  T356] [  778.805164] [  655.241173] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.151637][  T356]
> [  903.160126][  T528] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.166936][  T356] [  778.818740] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.166946][  T356]
> [  903.175785][  T528] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.185955][  T528] tasks-torture:torture_onoff task: online 0 failed: errno -5
> [  903.189448][  T356] [  778.825864] [  655.250559] [  531.607066] [  407.120936] tasks-torture:torture_onoff task: online 0 failed: errno -5
> 
> These multi-timestamp lines are odd. And they are almost exactly 124
> seconds apart.

Yup, this looks suspicious.

Here are my few ideas. Feel free to ignore them and do your own
debugging. I do not want to distract you.

The test produces the same messages over and over again. It is
possible that something has overflown after some amount of messages.
And the regular intervals are just a coincidence.

Are all messages broken this way?
Or does it start later?
Are this exact messages printed correctly at some points?

Is this console output? Or dmesg?

Are you able to reproduce it with the current Linus's master.
I wonder if it is something that we have already fixed.

Best Regards,
Petr