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Mon, 01 Jun 2026 02:57:41 -0700 (PDT) Received: from fedora ([149.3.87.76]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45ef34a03f8sm25589419f8f.7.2026.06.01.02.57.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Jun 2026 02:57:41 -0700 (PDT) From: Giorgi Tchankvetadze To: akpm@linux-foundation.org, vbabka@kernel.org Cc: surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Giorgi Tchankvetadze Subject: [PATCH] mm/compaction: guard move_freelist_head() against invalid freepage Date: Mon, 1 Jun 2026 17:39:42 +0400 Message-ID: <20260601133941.111989-2-giorgitchankvetadze1997@gmail.com> X-Mailer: git-send-email 2.52.0 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" In fast_isolate_freepages(), freepage is declared uninitialized and is only assigned a valid page pointer if list_for_each_entry_reverse exits via break. If the loop runs to completion (all pages in the freelist have pfn < min_pfn), freepage holds the list head sentinel and high_pfn remains zero, so the high_pfn fallback does not update it either. The subsequent unconditional call to move_freelist_head(freelist, freepage) then passes the sentinel as a page pointer, which is invalid. Guard move_freelist_head() inside the existing 'if (page)' block where freepage is guaranteed to refer to a real page. This issue was identified via Coccinelle (use_after_iter.cocci). Fixes: 5a811889de10 ("mm, compaction: use free lists to quickly locate a mi= gration target") Cc: stable@vger.kernel.org Signed-off-by: Giorgi Tchankvetadze --- mm/compaction.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 8f664fb09f24..320c082420fd 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1611,11 +1611,10 @@ static void fast_isolate_freepages(struct compact_c= ontrol *cc) freepage =3D page; } =20 - /* Reorder to so a future search skips recent pages */ - move_freelist_head(freelist, freepage); - - /* Isolate the page if available */ if (page) { + /* Reorder so a future search skips recent pages */ + move_freelist_head(freelist, freepage); + /* Isolate the page if available */ if (__isolate_free_page(page, order)) { set_page_private(page, order); nr_isolated =3D 1 << order; --=20 2.52.0