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Howlett" , Lorenzo Stoakes , Miaohe Lin , Michal Hocko , Mike Rapoport , Muchun Song , Nhat Pham , Oscar Salvador , Peter Xu , Roman Gushchin , Shakeel Butt , Shuah Khan , jthoughton@google.com, fvdl@google.com, rientjes@google.com, vannapurve@google.com, Suren Baghdasaryan , Vlastimil Babka , Wupeng Ma , Yanteng Si , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ackerley Tng , stable@vger.kernel.org Subject: Re: [PATCH 2/2] mm: hugetlb: Drop refcount before freeing on memcg charge failure Date: Fri, 4 Sep 2026 10:23:33 -0700 Message-ID: <20260904172334.322019-1-joshua.hahnjy@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260902-hugetlb-alloc-folio-memcg-charge-error-handling-v1-2-e3e8942c141b@google.com> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Wed, 02 Sep 2026 01:22:57 -0700 Ackerley Tng via B4 Relay wrote: > From: Ackerley Tng > > When mem_cgroup_charge_hugetlb(folio, gfp) returns -ENOMEM, the folio has > its refcount set to 1 via folio_ref_unfreeze(folio, 1). > > The error path calls free_huge_folio(folio) directly, which expects a > refcount of 0. Hence, VM_BUG_ON_FOLIO(folio_ref_count(folio), folio) is > triggered. > > Even with CONFIG_DEBUG_VM disabled, returning a folio with refcount 1 to > the freelist can corrupt allocator state later. > > Use folio_put(folio) instead of free_huge_folio(folio) to properly drop the > reference before freeing it. LGTM, thank you Ackerley! Reviewed-by: Joshua Hahn > Fixes: 991135774c0e0 ("memcg/hugetlb: introduce mem_cgroup_charge_hugetlb") > Cc: stable@vger.kernel.org > Signed-off-by: Ackerley Tng > Reviewed-by: Muchun Song > --- > mm/hugetlb.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 01b57f6d3b804..97c06f227ef8a 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -2889,7 +2889,7 @@ struct folio *hugetlb_alloc_folio(struct hstate *h, > lruvec_stat_mod_folio(folio, NR_HUGETLB, nr_pages); > > if (ret == -ENOMEM) { > - free_huge_folio(folio); > + folio_put(folio); > /* > * Skip uncharging hugetlb_cgroup since the charges > * were committed to the folio and freeing the folio > > -- > 2.55.0.970.g62bdec98f9-goog