linux-kernel - Re: [PATCH] selftest: mm: Test if hugepage does not get leaked during __bio_release

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Message-ID: <d551d1cd-a02f-42aa-9de2-10ff7757224c@redhat.com>
Date: Thu, 23 May 2024 22:40:25 +0200
From: David Hildenbrand <david@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
 Donet Tom <donettom@...ux.ibm.com>
Cc: Shuah Khan <shuah@...nel.org>, Matthew Wilcox <willy@...radead.org>,
 Tony Battersby <tonyb@...ernetics.com>, linux-mm@...ck.org,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
 Ritesh Harjani <ritesh.list@...il.com>, Mike Rapoport <rppt@...nel.org>,
 Muchun Song <songmuchun@...edance.com>, stable@...r.kernel.org
Subject: Re: [PATCH] selftest: mm: Test if hugepage does not get leaked during
 __bio_release_pages()

On 23.05.24 21:13, Andrew Morton wrote:
> On Thu, 23 May 2024 01:39:05 -0500 Donet Tom <donettom@...ux.ibm.com> wrote:
> 
>> Commit 1b151e2435fc ("block: Remove special-casing of compound
>> pages") caused a change in behaviour when releasing the pages
>> if the buffer does not start at the beginning of the page. This
>> was because the calculation of the number of pages to release
>> was incorrect.
>> This was fixed by commit 38b43539d64b ("block: Fix page refcounts
>> for unaligned buffers in __bio_release_pages()").
>>
>> We pin the user buffer during direct I/O writes. If this buffer is a
>> hugepage, bio_release_page() will unpin it and decrement all references
>> and pin counts at ->bi_end_io. However, if any references to the hugepage
>> remain post-I/O, the hugepage will not be freed upon unmap, leading
>> to a memory leak.
>>
>> This patch verifies that a hugepage, used as a user buffer for DIO
>> operations, is correctly freed upon unmapping, regardless of whether
>> the offsets are aligned or unaligned w.r.t page boundary.
>>
> 

Two SOF, is there a Co-developed-by: missing?

> You have stable@...r.kernel.org in the mail headers, so I assume you're
> proposing this for backporting.  When doing this, please include
> 
> Cc: <stable@...r.kernel.org>
> 
> in the changelog footers and also include a Fixes: target.  I'm
> assuming the suitable Fixes: target for this patch is 38b43539d64b?

This adds a new selfest to make sure what was fixed (and backported to 
stable) remains fixed.

-- 
Cheers,

David / dhildenb