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(c-67-164-59-41.hsd1.ca.comcast.net. [67.164.59.41]) by smtp.googlemail.com with ESMTPSA id 98e67ed59e1d1-30516d3ce04sm8074118a91.9.2025.03.31.19.11.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 31 Mar 2025 19:11:09 -0700 (PDT) From: "Vishal Moola (Oracle)" To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, muchun.song@linux.dev, "Vishal Moola (Oracle)" , Miaohe Lin , Oscar Salvador Subject: [PATCH] mm/compaction: Fix bug in hugetlb handling pathway Date: Mon, 31 Mar 2025 19:10:24 -0700 Message-ID: <20250401021025.637333-1-vishal.moola@gmail.com> X-Mailer: git-send-email 2.48.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The compaction code doesn't take references on pages until we're certain we should attempt to handle it. In the hugetlb case, isolate_or_dissolve_huge_page() may return -EBUSY without taking a reference to the folio associated with our pfn. If our folio's refcount drops to 0, compound_nr() becomes unpredictable, making low_pfn and nr_scanned unreliable. The user-visible effect is minimal - this should rarely happen (if ever). Fix this by storing the folio statistics earlier on the stack (just like the THP and Buddy cases). Also revert commit 66fe1cf7f581 ("mm: compaction: use helper compound_nr in isolate_migratepages_block") to make backporting easier. Fixes: 369fa227c219 ("mm: make alloc_contig_range handle free hugetlb pages= ") Cc: Miaohe Lin Cc: Oscar Salvador Signed-off-by: Vishal Moola (Oracle) Acked-by: Oscar Salvador --- mm/compaction.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 139f00c0308a..ca71fd3c3181 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -981,13 +981,13 @@ isolate_migratepages_block(struct compact_control *cc= , unsigned long low_pfn, } =20 if (PageHuge(page)) { + const unsigned int order =3D compound_order(page); /* * skip hugetlbfs if we are not compacting for pages * bigger than its order. THPs and other compound pages * are handled below. */ if (!cc->alloc_contig) { - const unsigned int order =3D compound_order(page); =20 if (order <=3D MAX_PAGE_ORDER) { low_pfn +=3D (1UL << order) - 1; @@ -1011,8 +1011,8 @@ isolate_migratepages_block(struct compact_control *cc= , unsigned long low_pfn, /* Do not report -EBUSY down the chain */ if (ret =3D=3D -EBUSY) ret =3D 0; - low_pfn +=3D compound_nr(page) - 1; - nr_scanned +=3D compound_nr(page) - 1; + low_pfn +=3D (1UL << order) - 1; + nr_scanned +=3D (1UL << order) - 1; goto isolate_fail; } =20 --=20 2.48.1