linux-kernel - Re: [PATCH v3] kho: init alloc tags when restoring pages from reserved memory

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Message-ID: <2vxzqzriaquh.fsf@kernel.org>
Date: Thu, 22 Jan 2026 10:23:18 +0000
From: Pratyush Yadav <pratyush@...nel.org>
To: ranxiaokai627@....com
Cc: akpm@...ux-foundation.org,  graf@...zon.com,  kent.overstreet@...ux.dev,
  kexec@...ts.infradead.org,  linux-kernel@...r.kernel.org,
  linux-mm@...ck.org,  pasha.tatashin@...een.com,  pratyush@...nel.org,
  ran.xiaokai@....com.cn,  rppt@...nel.org,  surenb@...gle.com
Subject: Re: [PATCH v3] kho: init alloc tags when restoring pages from
 reserved memory

Hi Ran,

On Thu, Jan 22 2026, ranxiaokai627@....com wrote:

>>> From: Ran Xiaokai <ran.xiaokai@....com.cn>
>>> 
>>> Memblock pages (including reserved memory) should have their allocation
>>> tags initialized to CODETAG_EMPTY via clear_page_tag_ref() before being
>>> released to the page allocator. When kho restores pages through
>>> kho_restore_page(), missing this call causes mismatched
>>> allocation/deallocation tracking and below warning message:
>>> 
>>> alloc_tag was not set
>>> WARNING: include/linux/alloc_tag.h:164 at ___free_pages+0xb8/0x260, CPU#1: swapper/0/1
>>> RIP: 0010:___free_pages+0xb8/0x260
>>>  kho_restore_vmalloc+0x187/0x2e0
>>>  kho_test_init+0x3c4/0xa30
>>>  do_one_initcall+0x62/0x2b0
>>>  kernel_init_freeable+0x25b/0x480
>>>  kernel_init+0x1a/0x1c0
>>>  ret_from_fork+0x2d1/0x360
>>> 
>>> Add missing clear_page_tag_ref() annotation in kho_restore_page() to
>>> fix this.
>>> 
>>> Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>
>>> ---
>>> It is based on linux-next 20260120. I dont konw whether this base is ok ?
>>
>>It's awkward.
>>
>>Your v2 patch was based on Linus mainline.  This is appropriate, as the
>>patch should be sent to Linus soon and it has cc:stable, so -stable
>>maintainers will try to backport it into earlier kernels.
>>
>>However your v3 patch is dependent upon other material ("kho: simplify
>>page initialization in kho_restore_page()") which is scheduled for
>>6.20(?)-rc1.
>
> I think i misunderstood Pratyush's last reply:
> "I suggested a re-roll of this patch based on top of my cleanup patches
> [1], since I think with those the end result is a bit nicer."

I was giving context to Andrew about the whole thing.

I thought it was a good idea when I suggested it to you, but at the time
I didn't think that this will go in the hotfixes branch. If it goes in
hotfixes, it doesn't make sense to base it on a series for the next
kernel.

Sorry for the confusion.

>
>>For a prompt, backportable merge it's best to base the fix on latest
>>Linus mainline, please.
>>
>>You didn't actually describe why v3 is different from v2.  If the
>>v2->v3 changes are just nice-to-have then let's redo those and base
>>them on linux-next in the usual fashion.
>
>>Unless I'm missing something, your well-reviewed, decently-tested v2
>>patch remains suitable for upstreaming during 6.18-rcX
>
> v2 version just fixed the folio case(compound page), but didn't fix the
> contiguous order 0 pages case. So i think it is better to send a v3 version
> base on lastest Linus tree and drop the v2 version.

Yep, that would be the idea. Resend the changes fixing both compound and
non-compound cases on top of Linus' tree and ignore my "simplify page
initialization" series.

And then I can later resend my series on top of your patch.

-- 
Regards,
Pratyush Yadav