linux-kernel - Re: [PATCH v2] mm/mmap: Regression fix for unmapped_area{

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Message-ID: <9460b08a-7740-42bd-8784-d27ea038e87b@gmail.com>
Date:   Mon, 15 May 2023 17:57:09 +0900
From:   Juhyung Park <qkrwngud825@...il.com>
To:     "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Michael Keyes <mgkeyes@...ovproductions.net>,
        Tad <support@...tco.us>, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        rick.p.edgecombe@...el.com
Subject: Re: [PATCH v2] mm/mmap: Regression fix for unmapped_area{_topdown}

Hi Liam,

It's a bit hard to follow this particular issue on v6.1 as there are 
many email threads related to this.

I just wanted to ask if whether this is fixed on mainline and v6.1 
stable yet.

If there's a new thread tackling this issue, I'd appreciate it if you 
can link it here.

Thanks,
regards

On 5/2/23 23:09, Liam R. Howlett wrote:
> ...Adding Rick to the Cc this time.
> 
> * Liam R. Howlett <Liam.Howlett@...cle.com> [230502 10:08]:
>> * Michael Keyes <mgkeyes@...ovproductions.net> [230430 18:41]:
>>> On 29.04.23 15:32, Tad wrote:
>>>> This reintroduces the issue described in
>>>> https://lore.kernel.org/linux-mm/cb8dc31a-fef2-1d09-f133-e9f7b9f9e77a@sony.com/
>>> Yes, I also ran into this (even though I'd somehow missed it the
>>> previous time).
>>
>> Rick Edgecombe reported something similar [1].
>>
>> This is probably to do with my stack guard checks I recently added.
>>
>>>
>>> Apparently the issue arises at mm/mmap.c:1582, where low_limit is set to
>>> vm_end_gap(tmp). Occasionally, this returns a 64-bit address (e.g.
>>> 0x7fedea581000), which is obviously greater than high_limit for a 32-bit
>>> mmap, and causes the next call to mas_empty_area() to fail.
>>>
>>> I'm not sure why vm_end_gap(tmp) occasionally returns a 64-bit address,
>>> or if the best solution is to just check for this and skip the retry if
>>> it occurs…
>>>
>>
>> Thanks for the debugging.  I will look into it.
>>
>> I am currently trying to revise how the iterators, prev/next deal with
>> shifting outside the requested limits.  I suspect it's something to do
>> with hitting the limit and what someone would assume the next operation
>> means.
>>
>> [1] https://lore.kernel.org/linux-mm/32f156ba80010fd97dbaf0a0cdfc84366608624d.camel@intel.com/
> 
>