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Subject: Re: [PATCH] m68k: mm: Remove check for VM_IO to fix deferred I/O
To:     Geert Uytterhoeven <geert@linux-m68k.org>,
        linux-m68k@lists.linux-m68k.org
References: <20220128173006.1713210-1-geert@linux-m68k.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org
From:   Michael Schmitz <schmitzmic@gmail.com>
Message-ID: <63c80eba-7c55-2a92-8078-c63cec3c9efb@gmail.com>
Date:   Sun, 30 Jan 2022 13:32:35 +1300
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Hi Geert,

testing this patch on my Falcon 030, I'm seeing a weird error checking 
and mounting the root filesystem (pata-falcon). The system appears to 
sit idle, never completing the journal recovery and mount. Still 
investigating that.

Can't see how that would be caused by your patch, just saying I could 
not yet test it.

Cheers,

	Michael


Am 29.01.2022 um 06:30 schrieb Geert Uytterhoeven:
> When an application accesses a mapped frame buffer backed by deferred
> I/O, it receives a segmentation fault.  Fix this by removing the check
> for VM_IO in do_page_fault().
>
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
> This check was never present in a fault handler on any other
> architecture than m68k.
> Some digging revealed that it was added in v2.1.106, but I couldn't find
> an email with a patch adding it.  That same kernel version extended the
> use of the hwreg_present() helper to HP9000/300, so the check might have
> been needed there, perhaps only during development?
> The Atari kernel relies heavily on hwreg_present() (both the success and
> failure cases), and these still work, at least on ARAnyM.
> ---
>  arch/m68k/mm/fault.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
> index 1493cf5eac1e7a39..71aa9f6315dc8028 100644
> --- a/arch/m68k/mm/fault.c
> +++ b/arch/m68k/mm/fault.c
> @@ -93,8 +93,6 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
>  	vma = find_vma(mm, address);
>  	if (!vma)
>  		goto map_err;
> -	if (vma->vm_flags & VM_IO)
> -		goto acc_err;
>  	if (vma->vm_start <= address)
>  		goto good_area;
>  	if (!(vma->vm_flags & VM_GROWSDOWN))
>