linux-kernel - Re: [PATCH] mm/khugepaged: Fix ->anon

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Message-ID: <4cb68043-1c06-6589-b83e-74847a06f457@redhat.com>
Date:   Tue, 24 Jan 2023 11:19:02 +0100
From:   David Hildenbrand <david@...hat.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>, g@....shutemov.name
Cc:     Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Zach O'Keefe <zokeefe@...gle.com>,
        linux-kernel@...r.kernel.org, Yang Shi <shy828301@...il.com>
Subject: Re: [PATCH] mm/khugepaged: Fix ->anon_vma race

On 24.01.23 01:51, Kirill A. Shutemov wrote:
> On Mon, Jan 23, 2023 at 12:07:05PM +0100, David Hildenbrand wrote:
>>>> commit bedf03416913d88c796288f9dca109a53608c745
>>>> Author: Yang Shi <shy828301@...il.com>
>>>> Date:   Wed Sep 7 11:01:44 2022 -0700
>>>>
>>>>       powerpc/64s/radix: don't need to broadcast IPI for radix pmd collapse flush
>>>>       The IPI broadcast is used to serialize against fast-GUP, but fast-GUP will
>>>>       move to use RCU instead of disabling local interrupts in fast-GUP.  Using
>>>>       an IPI is the old-styled way of serializing against fast-GUP although it
>>>>       still works as expected now.
>>>>       And fast-GUP now fixed the potential race with THP collapse by checking
>>>>       whether PMD is changed or not.  So IPI broadcast in radix pmd collapse
>>>>       flush is not necessary anymore.  But it is still needed for hash TLB.
>>>
>>> Okay. But I think tlb_remove_table_sync_one() belongs inside
>>> pmdp_collapse_flush(). Collapsing pmd table into huge page without
>>> serialization is a bug. They should not be separate.
>>
>> Agreed. But I wonder if it should be moved into a generic
>> pmdp_collapse_flush(), that calls an arch specific __pmdp_collapse_flush().
> 
> Um? There's no __pmdp_collapse_flush().

Did I imply that there is already one? ;)

-- 
Thanks,

David / dhildenb