Re: Further rcu stall on autobuilder

Richard Purdie

On Sun, 2021-05-23 at 12:51 -0400, Bruce Ashfield wrote:
On Sun, May 23, 2021 at 12:47 PM Richard Purdie
<richard.purdie@...> wrote:

We've got yet another rcu stall failure on the autobuilder:

and looking at the dmesg in the qemu log:

[ 20.424033] Freeing unused kernel image (rodata/data gap) memory: 652K
[ 20.425229] Run /sbin/init as init process
INIT: version 2.99 booting
FBIOPUT_VSCREENINFO failed, double buffering disabledStarting udev
[ 20.547298] udevd[161]: starting version 3.2.10
[ 20.553329] udevd[162]: starting eudev-3.2.10
[ 20.751260] EXT4-fs (vda): re-mounted. Opts: (null)
[ 20.752548] ext4 filesystem being remounted at / supports timestamps until 2038 (0x7fffffff)
INIT: Entering runlevel: 5
Configuring network interfaces... RTNETLINK answers: File exists
Starting random number generator daemon.
Starting OpenBSD Secure Shell server: sshd
Starting rpcbind daemon...done.
starting statd: done
Starting atd: OK
[ 21.921925] Installing knfsd (copyright (C) 1996 okir@...).
starting 8 nfsd kernel threads: [ 23.066283] NFSD: Using /var/lib/nfs/v4recovery as the NFSv4 state recovery directory
[ 23.068096] NFSD: Using legacy client tracking operations.
[ 23.069086] NFSD: starting 90-second grace period (net f0000098)
starting mountd: [ 45.272151] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[ 45.273423] rcu: 1-...0: (10 ticks this GP) idle=7ba/1/0x4000000000000000 softirq=598/612 fqs=5249
[ 45.274951] (detected by 2, t=21002 jiffies, g=-195, q=13)
[ 138.202149] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[ 332.762209] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:

This is with the kvm clock source disabled (in master-next) and with Bruce's
5.10.38 upgrade so that kind of rules out either of those two things for this
issue. It also can't be the qemu platform or cpu emulation used since we've
changed that.

What is really odd is that it never actually prints the stalled tasks. That
seems really strange. It is obviously alive enough to print a stall message
later but stalls out and is terminated after 1500s.

Really open to ideas at this point. Should we try a newer kernel version
for testing in -next, see if we can isolate this to 5.10?
If you want to switch to linux-yocto-dev, it is on 5.12.x, and I have
a local 5.13-rcX version of -dev.

We could whip together a SRCREV recipe for it, if you don't want to
use the AUTOREV.

I'm not going to do a full versioned linux-yocto for 5.12, but we can
special case this if we want to go that route.
A set of SRCREVs sounds like the best plan, I think it might be worth testing
to see if things improve or not.

What is also odd is that in that in that same build, another qemu instance
hung in syslinux loading bzImage. We've seen this before occasionally and
it seems to keep happening periodically. That would seem more like a qemu
bug yet we're on the latest qemu release :/.

In neither case did Randy's stall detector trigger as far as I can tell.



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