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Date:   Wed, 14 Jun 2023 11:30:11 +0100
From:   "Richard W.M. Jones" <rjones@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Aaron Thompson <dev@aaront.org>, linux-kernel@vger.kernel.org
Subject: Re: printk.time causes rare kernel boot hangs
Message-ID: <20230614103011.GL7912@redhat.com>
References: <20230613134105.GA10301@redhat.com>
 <20230614092158.GF1639749@hirez.programming.kicks-ass.net>
 <20230614094522.GA7636@redhat.com>
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OK I have a simpler test:

$ while true; do qemu-system-x86_64 -no-user-config -nodefaults -display none -machine accel=kvm:tcg,graphics=off -cpu max,la57=off -m 1280 -no-reboot -rtc driftfix=slew -no-hpet -global kvm-pit.lost_tick_policy=discard -kernel vmlinux -serial stdio -append "panic=1 console=ttyS0 edd=off udevtimeout=6000 udev.event-timeout=6000 no_timer_check printk.time=1 cgroup_disable=memory usbcore.nousb cryptomgr.notests tsc=reliable 8250.nr_uarts=1 root=UUID=7cd9caf4-6491-41a5-b387-38af6fa2d638 selinux=0 guestfs_verbose=1 TERM=xterm-256color" >& /tmp/log ; echo -n . ; done

where "vmlinux" is a locally compiled kernel with CONFIG_PRINTK_TIME=y
set.  I'm using the current git head.

This will print dots about once a second.  When it stops printing dots
(after potentially many thousands of iterations), take a look at
/tmp/log to see if it has hung at:

  [    0.071830] Freeing SMP alternatives memory: 48K

I tried connecting gdb to qemu but so far I've not successfully
managed to collect a usable stack trace.  I can't seem to get it to
print symbols, even though I believe I have disabled kASLR, but still
trying.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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