Bug 200957

Several Arch Linux users (including me) reported that since kernel 4.18 the booting process stalls under conditions which worked with earlier kernel versions. It happens very early, so nobody was able to get a dmesg output. Several users took photos and the kernel output was the same except for some numbers which may be irrelevant for you.

If I boot without "quiet" and with "debug", I see this:

(These five lines are from the init process of my initramfs:)
:: running early hook [udev]
starting version 239
:: running early hook [lvm2]
:: running hook [udev]
:: Triggering uevents...

(debug output with device info)

(And finally after about 60 seconds:)

INFO: rcu_preempt detected stalls on CPUs/tasks:
o1-...!: (0 ticks this GP) idle=cf0/0/0 softirq=90/90 fqs=0 last_accelerate: e833/e840, nonlazy_posted: 9306, ..
o(detected by 0, t=18062 jiffies, g=-244, c=-245, q=5)
Sending NMI from CPU0 to CPUs 1:
NMI backtrace for cpu1 skipped: idling at acpi_idle_do_entry+0x15/0x40
rcu_preempt kthread starved for 18062 jiffies! g18446744073709551372 c18446744073709551371 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=1
RCU grace-period kthread stack dump:
rcu_preempt	I	0	10	2 0x80000000
Call Trace:
 ? __schedule+0x29b/0x8b0
 schedule+0x32/0x90
 schedule_timeout+0x1d1/0x4a0
 ? collect_expired_timers+0xa0/0xa0
 rcu_gp_kthread+0x43e/0x950
 ? synchronize_rcu_expedited+0x30/0x30
 kthread+0x112/0x130
 ? kthread_flush_work_fn+0x10/0x10
 ret_from_fork+0x35/0x40

Two other users confirmed that they got the same call trace.

I was able to boot successfully with "acpi=off" or "nosmp"/"maxcpus=0" or "maxcpus=1", I used the last one several times to activate the second core later, and several other users could also boot with "nosmp" or used other parameters to boot successfully.

One other user and I used "git bisect" and we both got

7197e77abcb65a71d0b21d67beb24f153a96055e clocksource: Remove kthread

as first bad commit, which has been included since 4.18-rc1. All 4.18 releases up to 4.18.5 are affected, and I also tested 4.19-rc1 and found that it is affected.

The issue could possibly be restricted to old Intel Core 2 Duo CPUs and other CPUs of the same microarchitecture including Pentium models which I guess from looking at what other users wrote. I chose "x86-64" as Hardware because this is the only architecture which Arch Linux supports officially, so I assume that all affected Arch Linux users have this.

Here is the link to the forum thread:
https://bbs.archlinux.org/viewtopic.php?id=239672