Hi folks,
A few Fedora users have reported[0] a regression starting in v4.16.8 where the boot will hang ~1/3 of the time with the following RCU stall warning:
INFO: rcu_sched detected stalls on CPUs/tasks: o1-...!: (0 ticks this GP) idle=688/0/0 softirq=171/171 fqs=0 o(detected by 0, t=60002 jiffies, g=-142, c=-143, q=9) Sending NMI from CPU 0 to CPU 1: NMI backtrace for cpu 1 skipped: idling at acpi_processor_ffh_cstate_enter+0x65/0xb0 rcu_sched kthread starved for 60002 jiffies! g18446744073709551474 c1844674407370955143 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 -> cpu=1 RCU grace-period kthread stack dump: rcu_sched I 0 9 2 0x80000000 Call Trace: ? __schedule+0x234/0x850 schedule+0x28/0x80 schedule_timeout+0x166/0x380 ? __next_timer_interrupt+0xc0/0xc0 rcu_gp_kthread+0x368/0x830 ? rcu_process_callbacks+0x4f0/0x4f0 kthread+0x112/0x130 ? kthread_create_worker_on_cpu+0x70/0x70 ret_from_fork+0x35/0x40
A user has bisected the problem to the v4.16 commit 1ab4ca7c59d4 ("x86/tsc: Fix mark_tsc_unstable()"). According to the reporter, explicitly setting "tsc=" on the kernel command line causes the boot to always succeed. All the users have Thinkpad T500s or T400s (Core 2 Duos)
[0] https://bugzilla.redhat.com/show_bug.cgi?id=1579925
Thanks, Jeremy