On Wed, Oct 4, 2023 at 2:07 AM Mahesh J Salgaonkar wrote:
>
> On 2023-09-25 15:53:48 Mon, Pingfan Liu wrote:
> > paca_ptrs should be large enough to hold the boot_cpuid, hence, its
> > lower boundary is set to the bigger one between boot_cpuid+1 and
> > nr_cpus.
> >
> > On the other hand, some kernel component: -1. the timer assumes cpu0
> > online since the timer_list->flags subfield 'TIMER_CPUMASK' is zero if
> > not initialized to a proper present cpu. -2. power9_idle_stop() assumes
> > the primary thread's paca is allocated.
> >
> > Hence lift nr_cpu_ids from one to two to ensure cpu0 is onlined, if the
> > boot cpu is not cpu0.
> >
> > Result:
> > When nr_cpus=1, taskset -c 14 bash -c 'echo c > /proc/sysrq-trigger'
> > the kdump kernel brings up two cpus.
> > While when taskset -c 4 bash -c 'echo c > /proc/sysrq-trigger',
> > the kdump kernel brings up one cpu.
>
> I tried your changes on power9 and power10 systems. However, on power10 lpar I
> see bellow backtrace in kdump kernel bootup with nr_cpus=1.
>
Thanks for the testing. I have only tried this series on Power9 bare
metal. I think the bug is related with the code snippet in
update_mask_from_threadgroup()
for (i = first_thread; i < first_thread + threads_per_core; i++) {
int i_group_start = get_cpu_thread_group_start(i, tg);
^^^
Here it iterates over each thread in the core, but some of them are not online.
I will try to bring up a remedy.
Thanks,
Pingfan
> $ taskset -c 4 bash -c 'echo c > /proc/sysrq-trigger'
> [...]
> [0.00] Hardware name: IBM,9105-22A POWER10 (raw) 0x800200 0xf06
> of:IBM,FW1040.00 (NL1040_005) hv:phyp pSeries
> [0.00] printk: bootconsole [udbg0] enabled
> [0.00] the round shift between dt seq and the cpu logic number: 8
> [0.00] Partition configured for 16 cpus, operating system maximum is
> 2.
> [0.00] CPU maps initialized for 8 threads per core
> [...]
> [0.002249] BUG: Unable to handle kernel data access at 0x88c0
> [0.002260] Faulting instruction address: 0xc0001201226c
> [0.002268] Oops: Kernel access of bad area, sig: 11 [#1]
> [0.002274] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
> [0.002282] Modules linked in:
> [0.002288] CPU: 4 PID: 1 Comm: swapper/4 Not tainted 6.6.0-rc4 #1
> [0.002296] Hardware name: IBM,9105-22A POWER10 (raw) 0x800200 0xf06
> of:IBM,FW1040.00 (NL1040_005) hv:phyp pSeries
> [0.002305] NIP: c0001201226c LR: c00012012234 CTR:
> 0004
> [0.002312] REGS: c000167ff8f0 TRAP: 0380 Not tainted (6.6.0-rc4)
> [0.002321] MSR: 82009033 CR:
> 24000844 XER: 000a
> [0.002346] CFAR: c0001201231c IRQMASK: 0
> [0.002346] GPR00: c00012012234 c000167ffb90 c00011b61900
> 0002
> [0.002346] GPR04: 0001 0001
> c0004ffeff80
> [0.002346] GPR08: 0002
>
> [0.002346] GPR12: c00013141000 c00010011058
>
> [0.002346] GPR16:
>
> [0.002346] GPR20: 0028 c00012170968 c000120a3e80
> 0016
> [0.002346] GPR24: c0004ffdcfd0 c00012b82058
>
> [0.002346] GPR28: c0004fc80a68 c00012bf0350 c000120a3e2c
>
> [0.002426] NIP [c0001201226c] update_mask_from_threadgroup+0x98/0x174
> [0.002437] LR [c00012012234] update_mask_from_threadgroup+0x60/0x174
> [0.002444] Call Trace:
> [0.002451] [c000167ffb90] [c00012012234]
> update_mask_from_threadgroup+0x60/0x174 (unreliable)
> [0.002464] [c000167ffbe0] [c000120125f8]
> init_thread_group_cache_map+0x2b0/0x328
> [0.002477] [c000167ffc50] [c0001201296c]
> smp_prepare_cpus+0x2fc/0x4f0
> [0.002497] [c000167ffd10] [c00012004e40]
> kernel_init_freeable+0x198/0x3cc
> [0.002509] [c000167ffde0] [c00010011084] kernel_init+0x34/0x1b0
> [0.002531] [c000167ffe50] [c0001000dd3c]
> ret_from_kernel_user_thread+0x14/0x1c
> [0.002547] --- interrupt: 0 at 0x0
> [0.002553] NIP: LR: CTR:
>
> [0.002563] REGS: c000167ffe80 TRAP: Not tainted (6.6.0-rc4)
> [0.002569] MSR: <> CR: XER:
> [0.002576] CFAR: IRQMASK: 0
> [0.002576] GPR00:
>
> [0.002576] GPR04:
>
> [0.002576] GPR08:
>
> [0.002576] GPR12:
>
> [
