linux-kernel - Re: [PATCH V2 3/3] SH: cpuinfo: Fix a warning for CONFIG_CPUMASK

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Message-ID: <3a5a4bee5c0739a3b988a328376a6eed3c385fda.camel@physik.fu-berlin.de>
Date:   Wed, 08 Feb 2023 13:58:50 +0100
From:   John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To:     Huacai Chen <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>
Cc:     loongarch@...ts.linux.dev, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, Huacai Chen <chenhuacai@...il.com>,
        Guo Ren <guoren@...nel.org>, Xuerui Wang <kernel@...0n.name>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-mips@...r.kernel.org, linux-sh@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH V2 3/3] SH: cpuinfo: Fix a warning for
 CONFIG_CPUMASK_OFFSTACK

On Thu, 2022-07-14 at 16:41 +0800, Huacai Chen wrote:
> When CONFIG_CPUMASK_OFFSTACK and CONFIG_DEBUG_PER_CPU_MAPS is selected,
> cpu_max_bits_warn() generates a runtime warning similar as below while
> we show /proc/cpuinfo. Fix this by using nr_cpu_ids (the runtime limit)
> instead of NR_CPUS to iterate CPUs.
> 
> [    3.052463] ------------[ cut here ]------------
> [    3.059679] WARNING: CPU: 3 PID: 1 at include/linux/cpumask.h:108 show_cpuinfo+0x5e8/0x5f0
> [    3.070072] Modules linked in: efivarfs autofs4
> [    3.076257] CPU: 0 PID: 1 Comm: systemd Not tainted 5.19-rc5+ #1052
> [    3.099465] Stack : 9000000100157b08 9000000000f18530 9000000000cf846c 9000000100154000
> [    3.109127]         9000000100157a50 0000000000000000 9000000100157a58 9000000000ef7430
> [    3.118774]         90000001001578e8 0000000000000040 0000000000000020 ffffffffffffffff
> [    3.128412]         0000000000aaaaaa 1ab25f00eec96a37 900000010021de80 900000000101c890
> [    3.138056]         0000000000000000 0000000000000000 0000000000000000 0000000000aaaaaa
> [    3.147711]         ffff8000339dc220 0000000000000001 0000000006ab4000 0000000000000000
> [    3.157364]         900000000101c998 0000000000000004 9000000000ef7430 0000000000000000
> [    3.167012]         0000000000000009 000000000000006c 0000000000000000 0000000000000000
> [    3.176641]         9000000000d3de08 9000000001639390 90000000002086d8 00007ffff0080286
> [    3.186260]         00000000000000b0 0000000000000004 0000000000000000 0000000000071c1c
> [    3.195868]         ...
> [    3.199917] Call Trace:
> [    3.203941] [<90000000002086d8>] show_stack+0x38/0x14c
> [    3.210666] [<9000000000cf846c>] dump_stack_lvl+0x60/0x88
> [    3.217625] [<900000000023d268>] __warn+0xd0/0x100
> [    3.223958] [<9000000000cf3c90>] warn_slowpath_fmt+0x7c/0xcc
> [    3.231150] [<9000000000210220>] show_cpuinfo+0x5e8/0x5f0
> [    3.238080] [<90000000004f578c>] seq_read_iter+0x354/0x4b4
> [    3.245098] [<90000000004c2e90>] new_sync_read+0x17c/0x1c4
> [    3.252114] [<90000000004c5174>] vfs_read+0x138/0x1d0
> [    3.258694] [<90000000004c55f8>] ksys_read+0x70/0x100
> [    3.265265] [<9000000000cfde9c>] do_syscall+0x7c/0x94
> [    3.271820] [<9000000000202fe4>] handle_syscall+0xc4/0x160
> [    3.281824] ---[ end trace 8b484262b4b8c24c ]---
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> ---
>  arch/sh/kernel/cpu/proc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/sh/kernel/cpu/proc.c b/arch/sh/kernel/cpu/proc.c
> index a306bcd6b341..5f6d0e827bae 100644
> --- a/arch/sh/kernel/cpu/proc.c
> +++ b/arch/sh/kernel/cpu/proc.c
> @@ -132,7 +132,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>  
>  static void *c_start(struct seq_file *m, loff_t *pos)
>  {
> -	return *pos < NR_CPUS ? cpu_data + *pos : NULL;
> +	return *pos < nr_cpu_ids ? cpu_data + *pos : NULL;
>  }
>  static void *c_next(struct seq_file *m, void *v, loff_t *pos)
>  {

I build-tested the patch and also booted the patched kernel successfully
on my SH-7785LCR board.

Showing the contents of /proc/cpuinfo works fine, too:

root@...pitz:~> cat /proc/cpuinfo
machine         : SH7785LCR
processor       : 0
cpu family      : sh4a
cpu type        : SH7785
cut             : 7.x
cpu flags       : fpu perfctr llsc
cache type      : split (harvard)
icache size     : 32KiB (4-way)
dcache size     : 32KiB (4-way)
address sizes   : 32 bits physical
bogomips        : 599.99
root@...pitz:~>

Tested-by: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>

I am not sure yet whether the change is also correct as I don't know whether
it's possible to change the number of CPUs at runtime on SuperH.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
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