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t=1791903880; bh=r4WyTCLD/TtiSn6CjA6uGQFIb/xY+wFvIHGUv0Trrdo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=GVgbI6ap9ekVxLrxQcUPcwFnpUr5X7id2J6mNgSjf46AGprjLyPQ40B9VAgCg7Gru ztQ82X1+DIOx6V5ZFXZSotu8vj37Nbm+JnCvxJJADGCljW+QWlXV5ex1Jme50ZYGzB cNJGXj4nuYIeIMMGxAqRqkFNs9FdzidVUNeXRiN3ZUvunBQEBq32JGB6dOuwLCfphI 7sr1Yn48WwG47H5l8MJvGDbky0W+s6ylT4tkzk8juiZ4GYwkWVIsvcj7QK7+mCFVuD 0Ux9LYfe3FtOUl5lmlJ5kzWnqwx7LLb9uwbcXSi0m2gGtDAAOozgdDWYTS6gYnrIiR PhaWjPdBzCvNw== Message-ID: Date: Tue, 13 Oct 2026 17:04:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/hugetlb: fix max-only subpool accounting on alloc_hugetlb_folio failure To: Zhao Li , Andrew Morton Cc: mawupeng1@huawei.com, Muchun Song , Oscar Salvador , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260427145247.84157-2-enderaoelyther@gmail.com> <20260428030712.66256-2-enderaoelyther@gmail.com> <20260428113037.88766-2-enderaoelyther@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: D3B1A4000B X-Stat-Signature: 1wn7qd33ppc3x3kc59hp4sg67ej19wc4 X-HE-Tag: 1791903880-906683 X-HE-Meta: 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 lEy9JMIk /Por18aTkkfQkbY49DOgyQP25SEAVHmFUsUNcNg0BbaVNmzCDxzsBWt3+WpITZWeBtXDrXqmwrhEYwcQVoBxfdrMvEZi2r0DZTc/dHT4242T52ToWG+cg0neGgLS89KDfl0Wgzh87mZ/Kh7aYpequHD2WmZ/UAnikN2OSNUvxMDxUNxCKckHTtcJ5YnYpRKmBXU+7zyRxfd1QiFb+n6Is2ObpTN5ynNJhRi1BCpcgfbGe546Ws7v53/XZBDIO4TdQmz6F3UTgo3heXHmp1f2I+5TFU+0xx2kq9sK2eqiLnKShpExXVf498tL7JcVRu4ZoIKykIFtrzgmj24g1E9GH3NDRlyUZOgkBcoLO Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/28/26 13:30, Zhao Li wrote: > alloc_hugetlb_folio() calls hugepage_subpool_get_pages() when map_chg > is set. For a subpool with max_hpages != -1, that bumps used_hpages > regardless of whether it returns gbl_chg = 0 (rsv slot consumed) or > gbl_chg > 0 (used_hpages slot only). If the allocation later fails > before a folio is returned, the unwind must undo the used_hpages > bump. The old cleanup only ran for !gbl_chg, leaking used_hpages on > the gbl_chg > 0 path. > > For gbl_chg > 0 on max-only subpools (max_hpages != -1, min_hpages > == -1), hugepage_subpool_get_pages() took only a speculative > used_hpages slot. Drop that slot directly under spool->lock. In > that configuration hugepage_subpool_put_pages() cannot restore > rsv_hpages, so the direct decrement is the exact inverse and is > race-free against concurrent puts. This matches the used_hpages-only > part of hugetlb_reserve_pages()'s out_put_pages cleanup, but > restricts it to the max-only case where no rsv_hpages restoration is > possible. > > Mounts with min_hpages != -1 are left unchanged for now. v2's > approach (hugepage_subpool_put_pages() + h->resv_huge_pages++ to > back a restored rsv_hpages slot) double-counts global backing under > concurrent free_huge_folio() and creates phantom reservations under > concurrent hugetlb_unreserve_pages(). Safe cleanup of that quadrant > needs a coordinated fix across multiple call sites. > > Reproduced on size=20M hugetlbfs with the faulting task in a hugetlb > cgroup whose limit is exceeded. Vanilla leaks 6/8 hugepages of > subpool quota; this patch leaks 0/8. Verified under QEMU. > > Fixes: a833a693a490 ("mm: hugetlb: fix incorrect fallback for subpool") > Cc: stable@vger.kernel.org # v6.15+ > Signed-off-by: Zhao Li > --- > Changes in v3: > - Replace v2's hugepage_subpool_put_pages() + h->resv_huge_pages++ on > the gbl_chg > 0 branch with a direct used_hpages-- under spool->lock. > - Restrict the cleanup to (max_hpages != -1, min_hpages == -1) where > the direct decrement is the exact inverse of the speculative bump. > > Changes in v2: > - Skip the gbl_chg > 0 cleanup when max_hpages is unset. > - Add hugepage_subpool_put_pages() + h->resv_huge_pages++ on the > gbl_chg > 0 branch. > > mm/hugetlb.c | 25 ++++++++++++++++++------- > 1 file changed, 18 insertions(+), 7 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index f24bf49be047e..cfdeaf6394c5b 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -3025,13 +3025,24 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, > hugetlb_cgroup_uncharge_cgroup_rsvd(idx, pages_per_huge_page(h), > h_cg); > out_subpool_put: > - /* > - * put page to subpool iff the quota of subpool's rsv_hpages is used > - * during hugepage_subpool_get_pages. > - */ > - if (map_chg && !gbl_chg) { > - gbl_reserve = hugepage_subpool_put_pages(spool, 1); > - hugetlb_acct_memory(h, -gbl_reserve); > + if (map_chg) { I agree with Muchuns comment about removing the "gbl_chg > 0" check. You could consider the following structure, which reduces indentation and avoids touching the existing handling. if (map_chg && !gbl_chg) { ... } else if (map_chg && spool && spool->min_hpages == -1 && spool->max_hpages != -1) { ... } But the code would read a lot nicer as if (map_chg && !gbl_chg) { ... } else if (map_chg) { hugepage_subpool_XXX_pages() } Whereby the spool checks etc are handled in there. Muchun things that we might just be able to use hugepage_subpool_put_pages(). It that's possible, great. Otherwise create a new helper that wraps all the logic below. -- Cheers, David