linux-kernel - Re: [PATCH v6] mm/hugetlb: ignore hugepage kernel args if hugepages are unsupported

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Message-ID: <e97c41cd-44f7-4560-bc75-79283a438e91@kernel.org>
Date: Mon, 22 Dec 2025 11:54:46 +0100
From: "Christophe Leroy (CS GROUP)" <chleroy@...nel.org>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>,
 Sourabh Jain <sourabhjain@...ux.ibm.com>,
 "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Borislav Petkov <bp@...en8.de>, Heiko Carstens <hca@...ux.ibm.com>,
 Ingo Molnar <mingo@...hat.com>, Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Muchun Song <muchun.song@...ux.dev>,
 Oscar Salvador <osalvador@...e.de>, Thomas Gleixner <tglx@...utronix.de>,
 Vasily Gorbik <gor@...ux.ibm.com>, linux-mm@...ck.org,
 linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org, x86@...nel.org,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6] mm/hugetlb: ignore hugepage kernel args if hugepages
 are unsupported



Le 22/12/2025 à 11:28, David Hildenbrand (Red Hat) a écrit :
> On 12/22/25 06:57, Sourabh Jain wrote:
>>
>>
>> On 22/12/25 08:42, Ritesh Harjani (IBM) wrote:
>>> "David Hildenbrand (Red Hat)" <david@...nel.org> writes:
>>>
>>>>> Coming back to the fixes tag. I did mention a bit of a history [2] of
>>>>> whatever I could find while reviewing this patch. I am not sure 
>>>>> whether
>>>>> you have looked into the links shared in that email or not. Here [2]:
>>>>>
>>>>> [2]: https://eur01.safelinks.protection.outlook.com/? 
>>>>> url=https%3A%2F%2Flore.kernel.org%2Flinuxppc- 
>>>>> dev%2F875xa3ksz9.ritesh.list%40gmail.com%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cfe40f4881e8441ab3ebf08de4144e747%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639019961377096292%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=Dnvzy5kJ%2ByF9GJjIw%2B12FTjaVgeAM2gA9g7hsYl7Qok%3D&reserved=0
>>>>>
>>>>> Where I am coming from is.. The current patch is acutally a partial
>>>>> revert of the patch mentioned in the fixes tag. That means if this 
>>>>> patch
>>>>> gets applied to the older stable kernels, it would end up bringing the
>>>>> same problem back, which the "Fixes" tagged patch is fixing in the 1st
>>>>> place, isnt' it? See this discussion [3]...
>>>>>
>>>>> [3]: https://eur01.safelinks.protection.outlook.com/? 
>>>>> url=https%3A%2F%2Flore.kernel.org%2Fall%2Fb1f04f9f-fa46- 
>>>>> c2a0-7693-4a0679d2a1ee%40oracle.com%2FT%2F%23m0eee87b458d93559426b8b0e78dc6ebcd26ad3ae&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cfe40f4881e8441ab3ebf08de4144e747%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639019961377117150%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=bOO7FGN4jAtX3jjBnJVpSurmM9rGmz8vIs1iGtbm1gU%3D&reserved=0
>>>>>
>>>>> ... So, IMO - the right fixes tag, if we have to add, it should be the
>>>>> patch which moved the hpage_shift initialization to happen early 
>>>>> i.e. in
>>>>> mmu_early_init_devtree. That would be this patch [4]:
>>>>>
>>>>> [4]: https://eur01.safelinks.protection.outlook.com/? 
>>>>> url=https%3A%2F%2Fgit.kernel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Ftorvalds%2Flinux.git%2Fcommit%2F%3Fid%3D2354ad252b66695be02f4acd18e37bf6264f0464&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cfe40f4881e8441ab3ebf08de4144e747%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639019961377133860%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=0yTuECy%2BBGDLiSNYuqYH9xGBOSxiRLxAtW%2FWTQU%2FB%2BA%3D&reserved=0
>>>>>
>>>>> Now, it's not really that the patch [4] had any issue as such. But it
>>>>> seems like, that the current fix can only be applied after patch 
>>>>> [4] is
>>>>> taken.
>>>>>
>>>>> Do we agree?
>>>> I think we should document all that in the cover letter, an describe
>>>> that this partial revert is only possible after [4],
>>> Yes, I agree. Let's add the above details in the commit msg.
>>>
>>>> and that that must
>>>> be considered when attempting any kind of stable backports.
>>> Sure. I would prefer if we change the Fixes tag to the one which I
>>> pointed in above [4] (with explaination in the commit msg). However I am
>>> still ok if we would like to retain the existing fixes tag and show [4]
>>> as a dependency.
>>
>> I think we should keep the current Fixes tag with an explanation for
>> dependency
>> on [1] in the commit message.
>>
>> Would anyone have a different view?
> 
> Whatever introduced the issue should be called out in the Fixes tag; if 
> there are dependencies for the fix through other patches that were 
> already merged, that can be documented in the patch description 
> (relevant for stable or distro backports only).
> 

We can also use the Depends-on: tag, see for exemple commit 9517b82d8d42 
("nbd: defer config put in recv_work"):

     Reported-by: syzbot+56fbf4c7ddf65e95c7cc@...kaller.appspotmail.com
     Closes: 
https://lore.kernel.org/all/6907edce.a70a0220.37351b.0014.GAE@google.com/T/
     Fixes: 87aac3a80af5 ("nbd: make the config put is called before the 
notifying the waiter")
     Depends-on: e2daec488c57 ("nbd: Fix hungtask when nbd_config_put")
     Signed-off-by: Zheng Qixing <zhengqixing@...wei.com>
     Signed-off-by: Jens Axboe <axboe@...nel.dk>


Christophe