linux-kernel - Re: [PATCH 3/6] M68K: cpuinfo: Fix a warning for CONFIG_CPUMASK

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Message-ID: <CAMuHMdUazqHLbc80vpZ+Msg9A3j5aPJ3fx+CdCG3kuWDSf8WSw@mail.gmail.com>
Date:   Tue, 12 Jul 2022 10:28:25 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Huacai Chen <chenhuacai@...ngson.cn>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Michal Simek <monstr@...str.eu>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        loongarch@...ts.linux.dev, Linux-Arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <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>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        linux-um <linux-um@...ts.infradead.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH 3/6] M68K: cpuinfo: Fix a warning for CONFIG_CPUMASK_OFFSTACK

Hi Huacai,

Thanks for your patch!

On Tue, Jul 12, 2022 at 9:53 AM Huacai Chen <chenhuacai@...ngson.cn> wrote:
> When CONFIG_CPUMASK_OFFSTACK and CONFIG_DEBUG_PER_CPU_MAPS is selected,

DEBUG_PER_CPU_MAPS depends on SMP, which is not supported on m68k,
and thus cannot be enabled.

> 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

efivarfs on m68k?

EFIVAR_FS depends on EFI depends on !CPU_BIG_ENDIAN

> [    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>

Does this need a Fixes tag, so we know when the problem was introduced?

> --- a/arch/m68k/kernel/setup_no.c
> +++ b/arch/m68k/kernel/setup_no.c
> @@ -201,7 +201,7 @@ 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 ? ((void *) 0x12345678) : NULL;
> +       return *pos < nr_cpu_ids ? ((void *) 0x12345678) : NULL;
>  }

include/linux/cpumask.h has:

    #if NR_CPUS == 1
    #define nr_cpu_ids              1U

so on m68k, both evaluate to the same value?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds