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.
$ taskset -c 4 bash -c 'echo c > /proc/sysrq-trigger'
[...]
[ 0.000000] Hardware name: IBM,9105-22A POWER10 (raw) 0x800200 0xf000006 of:IBM,FW1040.00 (NL1040_005) hv:phyp pSeries
[ 0.000000] printk: bootconsole [udbg0] enabled
[ 0.000000] the round shift between dt seq and the cpu logic number: 8
[ 0.000000] Partition configured for 16 cpus, operating system maximum is 2.
[ 0.000000] CPU maps initialized for 8 threads per core
[...]
[ 0.002249] BUG: Unable to handle kernel data access at 0x88888888888888c0
[ 0.002260] Faulting instruction address: 0xc00000001201226c
[ 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 0xf000006 of:IBM,FW1040.00 (NL1040_005) hv:phyp pSeries
[ 0.002305] NIP: c00000001201226c LR: c000000012012234 CTR: 0000000000000004
[ 0.002312] REGS: c0000000167ff8f0 TRAP: 0380 Not tainted (6.6.0-rc4)
[ 0.002321] MSR: 8000000002009033 <SF,VEC,EE,ME,IR,DR,RI,LE> CR: 24000844 XER: 0000000a
[ 0.002346] CFAR: c00000001201231c IRQMASK: 0
[ 0.002346] GPR00: c000000012012234 c0000000167ffb90 c000000011b61900 0000000000000002
[ 0.002346] GPR04: 0000000000000000 0000000000000001 0000000000000001 c00000004ffeff80
[ 0.002346] GPR08: 0000000000000000 8888888888888888 0000000000000002 0000000000000000
[ 0.002346] GPR12: 0000000000000000 c000000013141000 c000000010011058 0000000000000000
[ 0.002346] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.002346] GPR20: 0000000000000028 c000000012170968 c0000000120a3e80 0000000000000016
[ 0.002346] GPR24: c00000004ffdcfd0 0000000000000000 c000000012b82058 0000000000000000
[ 0.002346] GPR28: c00000004fc80a68 c000000012bf0350 c0000000120a3e2c 0000000000000000
[ 0.002426] NIP [c00000001201226c] update_mask_from_threadgroup+0x98/0x174
[ 0.002437] LR [c000000012012234] update_mask_from_threadgroup+0x60/0x174
[ 0.002444] Call Trace:
[ 0.002451] [c0000000167ffb90] [c000000012012234] update_mask_from_threadgroup+0x60/0x174 (unreliable)
[ 0.002464] [c0000000167ffbe0] [c0000000120125f8] init_thread_group_cache_map+0x2b0/0x328
[ 0.002477] [c0000000167ffc50] [c00000001201296c] smp_prepare_cpus+0x2fc/0x4f0
[ 0.002497] [c0000000167ffd10] [c000000012004e40] kernel_init_freeable+0x198/0x3cc
[ 0.002509] [c0000000167ffde0] [c000000010011084] kernel_init+0x34/0x1b0
[ 0.002531] [c0000000167ffe50] [c00000001000dd3c] ret_from_kernel_user_thread+0x14/0x1c
[ 0.002547] --- interrupt: 0 at 0x0
[ 0.002553] NIP: 0000000000000000 LR: 0000000000000000 CTR: 0000000000000000
[ 0.002563] REGS: c0000000167ffe80 TRAP: 0000 Not tainted (6.6.0-rc4)
[ 0.002569] MSR: 0000000000000000 <> CR: 00000000 XER: 00000000
[ 0.002576] CFAR: 0000000000000000 IRQMASK: 0
[ 0.002576] GPR00: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.002576] GPR04: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.002576] GPR08: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.002576] GPR12: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.002576] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.002576] GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.002576] GPR24: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.002576] GPR28: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.002671] NIP [0000000000000000] 0x0
[ 0.002680] LR [0000000000000000] 0x0
[ 0.002689] --- interrupt: 0
[ 0.002697] Code: 7feafb78 813d0000 7d29fa14 7f895000 409d00d4 3ce20102 38e74758 79491f24 e87e0006 39000000 e8e70000 7d27482a <a8890038> 7f834000 79090020 419e005c
[ 0.002727] ---[ end trace 0000000000000000 ]---
[ 0.002739]
[ 1.002749] Kernel panic - not syncing: Fatal exception
[ 1.002795] Rebooting in 10 seconds..
Thanks,
-Mahesh.
>
> Signed-off-by: Pingfan Liu <piliu@xxxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
> Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> Cc: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxx>
> Cc: Wen Xiong <wenxiong@xxxxxxxxxx>
> Cc: Baoquan He <bhe@xxxxxxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Cc: kexec@xxxxxxxxxxxxxxxxxxx
> To: linuxppc-dev@xxxxxxxxxxxxxxxx
> ---
> arch/powerpc/kernel/paca.c | 10 ++++++----
> arch/powerpc/kernel/prom.c | 9 ++++++---
> 2 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
> index cda4e00b67c1..91e2401de1bd 100644
> --- a/arch/powerpc/kernel/paca.c
> +++ b/arch/powerpc/kernel/paca.c
> @@ -242,9 +242,10 @@ static int __initdata paca_struct_size;
>
> void __init allocate_paca_ptrs(void)
> {
> - paca_nr_cpu_ids = nr_cpu_ids;
> + int n = (boot_cpuid + 1) > nr_cpu_ids ? (boot_cpuid + 1) : nr_cpu_ids;
>
> - paca_ptrs_size = sizeof(struct paca_struct *) * nr_cpu_ids;
> + paca_nr_cpu_ids = n;
> + paca_ptrs_size = sizeof(struct paca_struct *) * n;
> paca_ptrs = memblock_alloc_raw(paca_ptrs_size, SMP_CACHE_BYTES);
> if (!paca_ptrs)
> panic("Failed to allocate %d bytes for paca pointers\n",
> @@ -287,13 +288,14 @@ void __init allocate_paca(int cpu)
> void __init free_unused_pacas(void)
> {
> int new_ptrs_size;
> + int n = (boot_cpuid + 1) > nr_cpu_ids ? (boot_cpuid + 1) : nr_cpu_ids;
>
> - new_ptrs_size = sizeof(struct paca_struct *) * nr_cpu_ids;
> + new_ptrs_size = sizeof(struct paca_struct *) * n;
> if (new_ptrs_size < paca_ptrs_size)
> memblock_phys_free(__pa(paca_ptrs) + new_ptrs_size,
> paca_ptrs_size - new_ptrs_size);
>
> - paca_nr_cpu_ids = nr_cpu_ids;
> + paca_nr_cpu_ids = n;
> paca_ptrs_size = new_ptrs_size;
>
> #ifdef CONFIG_PPC_64S_HASH_MMU
> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index 87272a2d8c10..15c994f54bf9 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -362,9 +362,12 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
> */
> boot_cpuid = i;
> found = true;
> - /* This works around the hole in paca_ptrs[]. */
> - if (nr_cpu_ids < nthreads)
> - set_nr_cpu_ids(nthreads);
> + /*
> + * Ideally, nr_cpus=1 can be achieved if each kernel
> + * component does not assume cpu0 is onlined.
> + */
> + if (boot_cpuid != 0 && nr_cpu_ids < 2)
> + set_nr_cpu_ids(2);
> }
> #ifdef CONFIG_SMP
> /* logical cpu id is always 0 on UP kernels */
> --
> 2.31.1
>
--
Mahesh J Salgaonkar
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