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Wed, 11 Nov 2026 08:32:32 +0000 X-Mizu-Trace-ID: 91f71c34f96ac602 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=utf-8 X-Archived-By: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3901.200.71.1.16\)) Subject: Re: [PATCH] mm/hugetlb_vmemmap: fix PMD split TLB flush race From: Muchun Song In-Reply-To: Date: Wed, 11 Nov 2026 16:32:14 +0800 Cc: Muchun Song , Oscar Salvador , Andrew Morton , David Hildenbrand , Mike Rapoport , Joao Martins , linux-mm@kvack.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <20261110112456.62827-1-songmuchun@bytedance.com> To: sashiko-reviews@lists.linux.dev X-Mailer: Apple Mail (2.3901.200.71.1.16) X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: A4FBD40005 X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: 5u3ag68fgmb1nkyj8k96dgou1yd5xwk3 X-HE-Tag: 1794385953-626630 X-HE-Meta: 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 2zZJZSIE PRm2Q9NFUBiMEZaMA+HgoEpIX+ANY+cxBAkGxrq86ecHsXuj7FLNnU0Qlth+8CFhe+z2WkLUlLJFNw2z+jdctnwYUsGHbA9EmlULOltkk+09ZSD8N+gNGITbgEEh9pdbuUiHWGJAKn/nTcHs7YFwVFWStSy2LCVqcyxkclUaF1a/ptup931WbHVjIVQHtyXrcvNUWl3M25ZZOaiyyC5STDizoA4h+NvnSgOKBLBSrsUlqvyy7dK7FrgByPzCK6MmQt8Bm2w5Y5242ADQRh0BiXCuXkbflVdWdsLOMsfqjBLHV7qRGwTuonglqxfFlpW7sTYX5O4PC7mJVfoVMffzqUmb1DbysL/Y23L07KTxiuSCIfFoHyP9/PTagTuZ5F34HyJkgDwKzQqMVFDydyxJqUCIfgROZKova8yIY Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 > On Nov 10, 2026, at 20:01, sashiko-bot@kernel.org wrote: >=20 > Thank you for your contribution! Sashiko AI review found 1 potential > issue to consider: > - [High] mm/hugetlb_vmemmap: deadlock from GFP_KERNEL alloc under > init_mm.mmap_lock > -- >=20 > commit c4de2ad9c999ebd1524c99a20d1c19a13ab7ec8f > Author: Muchun Song >=20 > mm/hugetlb_vmemmap: fix PMD split TLB flush race >=20 > This commit serializes batched vmemmap PMD splitting and its final TLB = flush > against concurrent PTE remapping using init_mm.mmap_lock. >=20 >> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c >> index ba8e11e399b24..ba6559bef742a 100644 >> --- a/mm/hugetlb_vmemmap.c >> +++ b/mm/hugetlb_vmemmap.c > [ ... ] >> @@ -559,6 +565,7 @@ void hugetlb_vmemmap_optimize_folios(struct = hstate *h, struct list_head *folio_l >> if (list_empty(folio_list)) >> return; >>=20 >> + mmap_write_lock(&init_mm); >> list_for_each_entry(folio, folio_list, lru) { >> int ret; >>=20 >=20 > [Severity: High] > Can holding init_mm.mmap_lock for write across = hugetlb_vmemmap_pteify_folio() > deadlock in memory reclaim? A valid point, I'll fix it ASAP. THanks. >=20 > hugetlb_vmemmap_pteify_folio() walks the kernel page tables and calls > vmemmap_split_pmd() -> pte_alloc_one_kernel(&init_mm), which allocates = a page > table with GFP_PGTABLE_KERNEL (GFP_KERNEL). Reclaim shrinkers such as > ttm_pool_shrinker_scan() take mmap_read_lock(&init_mm) when restoring = direct > map attributes via set_pages_wb() -> change_page_attr_set_clr(): >=20 > hugetlb_vmemmap_optimize_folios() > mmap_write_lock(&init_mm) > hugetlb_vmemmap_pteify_folio() > ... > vmemmap_split_pmd() > pte_alloc_one_kernel(&init_mm) /* GFP_KERNEL */ > > ttm_pool_shrinker_scan() > ... > change_page_attr_set_clr() > mmap_read_lock(&init_mm) <-- self-deadlock >=20 > Because fs_reclaim nests outside init_mm.mmap_lock, this also triggers = a > lockdep splat on the first vmemmap PMD split (including under > mmap_read_lock(&init_mm) in vmemmap_optimize_folio()) and can ABBA = deadlock > against kswapd. >=20 > --=20 > Sashiko AI review =C2=B7 = https://sashiko.dev/#/patchset/20261110112456.62827-1-songmuchun@bytedance= .com?part=3D1