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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 15 May 2023 11:38:40 +0200
Message-ID: <CAMuHMdXqgzh-_zwirAB+FXSZbuJ6WpML_kMdTRUD_=-Rpx0T5w@mail.gmail.com>
Subject: Re: [PATCH] nubus: Partially revert proc_create_single_data() conversion
To:     Finn Thain <fthain@linux-m68k.org>
Cc:     Christoph Hellwig <hch@lst.de>, stable@vger.kernel.org,
        linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org
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On Tue, Mar 14, 2023 at 9:53 AM Finn Thain <fthain@linux-m68k.org> wrote:
> The conversion to proc_create_single_data() introduced a regression
> whereby reading a file in /proc/bus/nubus results in a seg fault:
>
>  # grep -r . /proc/bus/nubus/e/
> Data read fault at 0x00000020 in Super Data (pc=0x1074c2)
> BAD KERNEL BUSERR
> Oops: 00000000
> Modules linked in:
> PC: [<001074c2>] PDE_DATA+0xc/0x16
> SR: 2010  SP: 38284958  a2: 01152370
> d0: 00000001    d1: 01013000    d2: 01002790    d3: 00000000
> d4: 00000001    d5: 0008ce2e    a0: 00000000    a1: 00222a40
> Process grep (pid: 45, task=142f8727)
> Frame format=B ssw=074d isc=2008 isb=4e5e daddr=00000020 dobuf=01199e70
> baddr=001074c8 dibuf=ffffffff ver=f
> Stack from 01199e48:
>         01199e70 00222a58 01002790 00000000 011a3000 01199eb0 015000c0 00000000
>         00000000 01199ec0 01199ec0 000d551a 011a3000 00000001 00000000 00018000
>         d003f000 00000003 00000001 0002800d 01052840 01199fa8 c01f8000 00000000
>         00000029 0b532b80 00000000 00000000 00000029 0b532b80 01199ee4 00103640
>         011198c0 d003f000 00018000 01199fa8 00000000 011198c0 00000000 01199f4c
>         000b3344 011198c0 d003f000 00018000 01199fa8 00000000 00018000 011198c0
> Call Trace: [<00222a58>] nubus_proc_rsrc_show+0x18/0xa0
>  [<000d551a>] seq_read+0xc4/0x510
>  [<00018000>] fp_fcos+0x2/0x82
>  [<0002800d>] __sys_setreuid+0x115/0x1c6
>  [<00103640>] proc_reg_read+0x5c/0xb0
>  [<00018000>] fp_fcos+0x2/0x82
>  [<000b3344>] __vfs_read+0x2c/0x13c
>  [<00018000>] fp_fcos+0x2/0x82
>  [<00018000>] fp_fcos+0x2/0x82
>  [<000b8aa2>] sys_statx+0x60/0x7e
>  [<000b34b6>] vfs_read+0x62/0x12a
>  [<00018000>] fp_fcos+0x2/0x82
>  [<00018000>] fp_fcos+0x2/0x82
>  [<000b39c2>] ksys_read+0x48/0xbe
>  [<00018000>] fp_fcos+0x2/0x82
>  [<000b3a4e>] sys_read+0x16/0x1a
>  [<00018000>] fp_fcos+0x2/0x82
>  [<00002b84>] syscall+0x8/0xc
>  [<00018000>] fp_fcos+0x2/0x82
>  [<0000c016>] not_ext+0xa/0x18
> Code: 4e5e 4e75 4e56 0000 206e 0008 2068 ffe8 <2068> 0020 2008 4e5e 4e75 4e56 0000 2f0b 206e 0008 2068 0004 2668 0020 206b ffe8
> Disabling lock debugging due to kernel taint
>
> Segmentation fault
>
> The proc_create_single_data() conversion does not work because
> single_open(file, nubus_proc_rsrc_show, PDE_DATA(inode)) is not
> equivalent to the original code.
>
> Fixes: 3f3942aca6da ("proc: introduce proc_create_single{,_data}")
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: stable@vger.kernel.org # 5.6+
> Signed-off-by: Finn Thain <fthain@linux-m68k.org>

Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
i.e. will queue in the m68k for-v6.5 branch.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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