linux-kernel - Re: [PATCH] mm/khugepaged: Fix race with folio splitting in hpage_collapse_scan

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Message-ID: <231ebbc1-2110-4d82-b4e9-5a1b1220d9c4@amd.com>
Date: Fri, 23 May 2025 13:20:55 +0530
From: Shivank Garg <shivankg@....com>
To: Dev Jain <dev.jain@....com>, akpm@...ux-foundation.org, david@...hat.com,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc: ziy@...dia.com, baolin.wang@...ux.alibaba.com,
 lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, npache@...hat.com,
 ryan.roberts@....com, fengwei.yin@...el.com, bharata@....com,
 syzbot+2b99589e33edbe9475ca@...kaller.appspotmail.com
Subject: Re: [PATCH] mm/khugepaged: Fix race with folio splitting in
 hpage_collapse_scan_file()



On 5/22/2025 3:37 PM, Dev Jain wrote:
> 
> On 22/05/25 3:04 pm, Shivank Garg wrote:
>> folio_mapcount() checks folio_test_large() before proceeding to
> 
> 
> It is not very clear in the description, where is this folio_mapcount() call present?
> 
> Are you talking about is_refcount_suitable()?

Yes, The issue originates from is_refcount_suitable(), which internally relies on folio_mapcount(), which contain the race.

I'll update the description to make it clearer.

Thanks,
Shivank