linux-kernel - Re: [PATCH v1 07/11] mm/huge_memory: convert split_huge_pages_pid() from follow_page() to folio

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <a5f059a0-32d6-453e-9d18-1f3bfec3a762@redhat.com>
Date: Tue, 6 Aug 2024 12:03:25 +0200
From: David Hildenbrand <david@...hat.com>
To: Ryan Roberts <ryan.roberts@....com>, linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, linux-doc@...r.kernel.org, kvm@...r.kernel.org,
 linux-s390@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Jonathan Corbet <corbet@....net>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>, Heiko Carstens
 <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>,
 Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
 Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v1 07/11] mm/huge_memory: convert split_huge_pages_pid()
 from follow_page() to folio_walk

On 06.08.24 11:56, David Hildenbrand wrote:
> On 06.08.24 11:46, Ryan Roberts wrote:
>> On 02/08/2024 16:55, David Hildenbrand wrote:
>>> Let's remove yet another follow_page() user. Note that we have to do the
>>> split without holding the PTL, after folio_walk_end(). We don't care
>>> about losing the secretmem check in follow_page().
>>
>> Hi David,
>>
>> Our (arm64) CI is showing a regression in split_huge_page_test from mm selftests from next-20240805 onwards. Navigating around a couple of other lurking bugs, I was able to bisect to this change (which smells about right).
>>
>> Newly failing test:
>>
>> # # ------------------------------
>> # # running ./split_huge_page_test
>> # # ------------------------------
>> # # TAP version 13
>> # # 1..12
>> # # Bail out! Still AnonHugePages not split
>> # # # Planned tests != run tests (12 != 0)
>> # # # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
>> # # [FAIL]
>> # not ok 52 split_huge_page_test # exit=1
>>
>> It's trying to split some pmd-mapped THPs then checking and finding that they are not split. The split is requested via /sys/kernel/debug/split_huge_pages, which I believe ends up in this function you are modifying here. Although I'll admit that looking at the change, there is nothing obviously wrong! Any ideas?
> 
> Nothing jumps at me as well. Let me fire up the debugger :)

Ah, very likely the can_split_folio() check expects a raised refcount 
already.

-- 
Cheers,

David / dhildenb