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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>
 <63c80eba-7c55-2a92-8078-c63cec3c9efb@gmail.com>
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: <8913a0a2-9496-143c-18c2-f3023fd37ba0@gmail.com>
Date:   Sun, 30 Jan 2022 19:57:34 +1300
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Hi Geert,

Am 30.01.2022 um 13:32 schrieb Michael Schmitz:
> 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.

Belay that - not related to your patch, must be some other regression 
since v5.16 that I'm seeing there.

Just ignore the noise ...

Cheers,

	Michael


> 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))
>>