Subject: Re: [PATCH] powerpc/pseries/cpuhp: Use alloc_cpumask_var() in pseries_cpu_hotplug_init()

From: Nathan Lynch <[email-masked]>
Date: Mon, 08 Nov 2021 17:06:29 -0600

Waiman Long <[email-masked]> writes:

> It was found that the following warning message could be printed out when
> booting the kernel on PowerPC systems that support LPAR:
>
> [    0.129584] WARNING: CPU: 0 PID: 1 at mm/memblock.c:1451 memblock_alloc_internal+0x5c/0x104
> [    0.129593] Modules linked in:
> [    0.129598] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.14.0-11.el9.ppc64le+debug #1
> [    0.129605] NIP:  c000000002040134 LR: c00000000204011c CTR: c0000000020241a8
> [    0.129610] REGS: c000000005637760 TRAP: 0700   Not tainted  (5.14.0-11.el9.ppc64le+debug)
> [    0.129616] MSR:  8000000002029033 <SF,VEC,EE,ME,IR,DR,RI,LE>  CR: 48000222  XER: 00000002
> [    0.129635] CFAR: c0000000004d1cf4 IRQMASK: 0
> [    0.129635] GPR00: c00000000204011c c000000005637a00 c000000002c94d00 0000000000000001
> [    0.129635] GPR04: 0000000000000080 0000000000000000 0000000000000000 ffffffffffffffff
> [    0.129635] GPR08: 0000000000000000 0000000000000003 c00000000205ac64 0000000000080000
> [    0.129635] GPR12: 0000000000000000 c0000000049d0000 c000000000013078 0000000000000000
> [    0.129635] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> [    0.129635] GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> [    0.129635] GPR24: c000000002003808 c00000000146f7b8 0000000000000000 0000000000000100
> [    0.129635] GPR28: c000000002d7cf80 0000000000000000 0000000000000008 0000000000000000
> [    0.129710] NIP [c000000002040134] memblock_alloc_internal+0x5c/0x104
> [    0.129717] LR [c00000000204011c] memblock_alloc_internal+0x44/0x104
> [    0.129723] Call Trace:
> [    0.129726] [c000000005637a00] [c000000005637a40] 0xc000000005637a40 (unreliable)
> [    0.129735] [c000000005637a60] [c0000000020404d8] memblock_alloc_try_nid+0x94/0xcc
> [    0.129743] [c000000005637af0] [c00000000205ac64] alloc_bootmem_cpumask_var+0x4c/0x9c
> [    0.129751] [c000000005637b60] [c0000000020242e0] __machine_initcall_pseries_pseries_cpu_hotplug_init+0x138/0x1d8
> [    0.129760] [c000000005637bf0] [c000000000012404] do_one_initcall+0xa4/0x4f0
> [    0.129768] [c000000005637cd0] [c000000002005358] do_initcalls+0x140/0x18c
> [    0.129776] [c000000005637d80] [c0000000020055b8] kernel_init_freeable+0x178/0x1d0
> [    0.129783] [c000000005637db0] [c0000000000130a0] kernel_init+0x30/0x190
> [    0.129790] [c000000005637e10] [c00000000000cef4] ret_from_kernel_thread+0x5c/0x64
>
> The warning is printed in memblock_alloc_internal() because the slab
> has been initialized when the initcalls are being processed.

Looks like CONFIG_CPUMASK_OFFSTACK=y is necessary for the warning to
trigger... guess that explains how it's escaped notice.

> To
> avoid the warning, change alloc_bootmem_cpumask_var() call in
> pseries_cpu_hotplug_init() to alloc_cpumask_var() instead. Also
> change cpumask_or() to cpumask_copy() or we will have to use
> zalloc_cpumask_var().

Makes sense.

> Fixes: bd1dd4c5f528 ("powerpc/pseries: Prevent free CPU ids being reused on another node")
> Signed-off-by: Waiman Long <[email-masked]>
> ---
>  arch/powerpc/platforms/pseries/hotplug-cpu.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
> index 5ab44600c8d3..e8e08d916b16 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
> @@ -864,12 +864,12 @@ static int __init pseries_cpu_hotplug_init(void)
>  	/* Processors can be added/removed only on LPAR */
>  	if (firmware_has_feature(FW_FEATURE_LPAR)) {
>  		for_each_node(node) {
> -			alloc_bootmem_cpumask_var(&node_recorded_ids_map[node]);
> +			alloc_cpumask_var(&node_recorded_ids_map[node],
> +					  GFP_KERNEL|GFP_NOWAIT);

This isn't atomic context, so GFP_KERNEL alone should be used.

Otherwise this change looks right to me.

>  
>  			/* Record ids of CPU added at boot time */
> -			cpumask_or(node_recorded_ids_map[node],
> -				   node_recorded_ids_map[node],
> -				   cpumask_of_node(node));
> +			cpumask_copy(node_recorded_ids_map[node],
> +				     cpumask_of_node(node));
>  		}
>  
>  		of_reconfig_notifier_register(&pseries_smp_nb);
> -- 
> 2.27.0