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([213.165.253.80]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-3a16b1a98dfsm3389391fa.21.2026.08.17.03.34.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Aug 2026 03:34:35 -0700 (PDT) From: Narek Jilavyan To: Muchun Song , Oscar Salvador , Andrew Morton Cc: David Hildenbrand , Shakeel Butt , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Narek Jilavyan Subject: [PATCH] mm/hugetlb_cgroup: call page_counter_set_max() outside VM_BUG_ON() Date: Mon, 17 Aug 2026 10:34:33 +0000 Message-ID: <20260817103433.191266-1-njilav@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit hugetlb_cgroup_css_alloc() rounds the counter limit down to a multiple of the huge page size and then applies it inside an assertion: VM_BUG_ON(page_counter_set_max(fault, limit)); VM_BUG_ON(page_counter_set_max(rsvd, limit)); With CONFIG_DEBUG_VM=n, VM_BUG_ON(cond) is BUILD_BUG_ON_INVALID(cond), i.e. ((void)(sizeof((__force long)(cond)))), whose operand is never evaluated. page_counter_set_max() is not a predicate - it performs xchg(&counter->max, nr_pages) - so on every non-debug kernel the limit is never applied and the counters keep page_counter_init()'s PAGE_COUNTER_MAX. That is user-visible, because hugetlb_cgroup_read_u64_max() recomputes the same rounded value and uses equality as its "unlimited" sentinel. PAGE_COUNTER_MAX is LONG_MAX / PAGE_SIZE = 2251799813685247, which is odd, so round_down() really does change it and the two sides disagree. With CONFIG_DEBUG_VM=n: $ cat /sys/fs/cgroup/t/hugetlb.2MB.max 9223372036854771712 and with this patch: $ cat /sys/fs/cgroup/t/hugetlb.2MB.max max A debug option should not change cgroup output. Call the function, then assert the result, as v6.12 did. Use VM_WARN_ON_ONCE() rather than restoring VM_BUG_ON(): the two are identical under CONFIG_DEBUG_VM=n, and checkpatch asks that new code not use BUG() variants. Fixes: 0e2759afcaf9 ("page_counter: track failcnt only for legacy cgroups") Signed-off-by: Narek Jilavyan --- mm/hugetlb_cgroup.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c index e0083de1ca..ecb6e0b781 100644 --- a/mm/hugetlb_cgroup.c +++ b/mm/hugetlb_cgroup.c @@ -97,6 +97,7 @@ static void hugetlb_cgroup_init(struct hugetlb_cgroup *h_cgroup, struct page_counter *fault, *fault_parent = NULL; struct page_counter *rsvd, *rsvd_parent = NULL; unsigned long limit; + int ret; if (parent_h_cgroup) { fault_parent = hugetlb_cgroup_counter_from_cgroup( @@ -118,8 +119,10 @@ static void hugetlb_cgroup_init(struct hugetlb_cgroup *h_cgroup, limit = round_down(PAGE_COUNTER_MAX, pages_per_huge_page(&hstates[idx])); - VM_BUG_ON(page_counter_set_max(fault, limit)); - VM_BUG_ON(page_counter_set_max(rsvd, limit)); + ret = page_counter_set_max(fault, limit); + VM_WARN_ON_ONCE(ret); + ret = page_counter_set_max(rsvd, limit); + VM_WARN_ON_ONCE(ret); } } -- 2.43.0