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

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Date: Thu, 23 May 2024 12:13:44 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: 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>, David Hildenbrand <david@...hat.com>,
 stable@...r.kernel.org
Subject: Re: [PATCH] selftest: mm: Test if hugepage does not get leaked
 during __bio_release_pages()

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.
> 

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?