From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794273133; b=eHuh4bX2yr0qY/wYPZngumOfOBlr0Dpj4Oe/BsKZ5y/JLAZ8WBHBjzBHpNlyy8htLLLT 3Ul44OVYDzfLrIXwN1U1X9mLXhe5V6sc/RWjy2PO0vxSZsqWdH0ZnutI1sFakXoaimUxu xvnBFxCZkoFger/oQ1WVeLfHXYMA+uwzngZL3yX4ims7XFyBqcjFdyfStrR9/t5kYw0JI U68LdgY2cBWAVsc70ZKYdu2s/LWfMDDQFeHNUvc8Dpw054k/dWwWG9kVEUJ3YF5qGyJpo 9N2+uHJyJd9Nr0nHDdgqIzO397N1dn2hQ0BBuSWZbcljEIQ5jHBdEzg2fqoBE36Kxkg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794273133; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=+LIIqpw5uo6EtBDedpjTb2CrFPDd+rtBls0f20y4ksw=; b=MSI6D0N2oiZIyBNIvRLxaCo0NTT2eSFjRQDTIvJRKDcmAomdZFsEomOymiUIOlSY9thQ uJHQ5BkJGZ3UODfa9i4ouo9lybI4hqrFiXPkzcyLU2LLlX6F56+32XJuNGpsUNzMciSIo j3M2cZXxVI3N/T9anoaH+LkszP7bhqQ5ODfmrusnxoxc9BWsBow67oKLDezMzkB5bBv8d ePmqeuBYMxWhPB4SEkp33XgOJtG0l7MQ2lVH1UCa90bWjeECPuSiMB8z1yANsQuHgGzVZ ccvCTMrfk7xQa/C9JydbMjL2Ih4GZXAi0KhplMhf6Z08BKOhXuwe/5F8bEgf5KU1gqg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=ILBBnIIR; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1A386606A31C for ; Tue, 10 Nov 2026 01:12:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=ILBBnIIR Received: by smtp.kernel.org (Postfix) with ESMTPSA id DD1B51F0089F; Tue, 10 Nov 2026 01:12:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794273133; bh=+LIIqpw5uo6EtBDedpjTb2CrFPDd+rtBls0f20y4ksw=; h=From:To:Cc:Subject:Date; b=ILBBnIIRVJblXkdlzf/Fz3jjR7Bo3GgfyQN3pkSwIlNtuApFdLL+cXczwnTdDif7w LNQP6Sit9UxH9tlnjbpvuAgGwpTkI7Ukb7e0EAeaA2zz7Ok0UUo1u/N/NCNd1FzLx2 e9P+0+G3/uI1JFv6MxW9tXH2NWnq0SOkgyxEalOcLKNIiB0691seLBy5b4K+CCoTkR wDne6oOhlJg2onEVW8k4qt+YU1+VyksFPzys3iAu+3JCCP2PMQGUOIj66MB1tNNjBq tkGAvLIpd1FADMJz9ajqdx/7BqjfsT5EmEnu4IY/pXcjjUVdnKmx0Bgvjsso1sNBvN XgukSAloPWHYw== From: Sasha Levin To: lizhe.67@bytedance.com, david@kernel.org, akpm@linux-foundation.org, muchun.song@linux.dev, osalvador@suse.de, peterx@redhat.com, rppt@kernel.org, azpijr@gmail.com Cc: stable@vger.kernel.org Subject: FAILED: patch "[PATCH] mm/hugetlb: fix mremap deadlock when PMD sharing is possible" failed to apply to 6.6-stable tree Date: Mon, 9 Nov 2026 20:12:10 -0500 Message-ID: <20261109201210-failed-6.6-92daa8652f88@kernel.org> X-Mailer: git-send-email 2.53.0 X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 92daa8652f88c8cfc05f4899a8408a04b02f211e # git commit -s git send-email --to '' --in-reply-to '20261109201210-failed-6.6-92daa8652f88@kernel.org' --subject-prefix 'PATCH 6.6.y' 'HEAD^..' Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From 92daa8652f88c8cfc05f4899a8408a04b02f211e Mon Sep 17 00:00:00 2001 From: Li Zhe Date: Thu, 22 Oct 2026 11:45:43 +0800 Subject: [PATCH] mm/hugetlb: fix mremap deadlock when PMD sharing is possible move_hugetlb_page_tables() holds the mapping's i_mmap_rwsem for write while moving hugetlb PTEs. This prevents races with truncation and protects huge_pmd_unshare(), but the move loop must not call helpers that can acquire the same rwsem for read. huge_pte_alloc() can do that when the destination can use PMD sharing: it may call huge_pmd_share(), which takes i_mmap_rwsem for read while searching for a shareable PMD table. Calling it while the move path already holds i_mmap_rwsem for write can deadlock. Avoid that path for PMD-sized hugetlb mappings that can use PMD sharing. Instead of allocating or sharing the destination page table while moving, zap the source range and let the destination fault path populate or share the PMD lazily. Reuse the hugetlb unmap logic for the source-side zap by splitting the core loop out of __unmap_hugepage_range(). The wrapper keeps the existing tlb_start_vma(), tlb_end_vma() and huge_pmd_unshare_flush() behavior, while move_hugetlb_page_tables() can reuse the unmap loop with its existing mmu_gather. Link: https://lore.kernel.org/20261022034543.51226-4-lizhe.67@bytedance.com Fixes: 550a7d60bd5e ("mm, hugepages: add mremap() support for hugepage backed vma") Signed-off-by: Li Zhe Co-developed-by: David Hildenbrand (Arm) Signed-off-by: David Hildenbrand (Arm) Signed-off-by: Andrew Morton Cc: Muchun Song Cc: Oscar Salvador Cc: Peter Xu Cc: Mike Rapoport Cc: Jose A. Perez de Azpillaga Cc: --- mm/hugetlb.c | 47 +++++++++++++++++++++++++++++++++++++---------- 1 file changed, 37 insertions(+), 10 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 8995f4cc4e65d..ec05e8c1d1f85 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -137,6 +137,10 @@ static int __huge_pmd_unshare(struct mmu_gather *tlb, bool check_locks); static void hugetlb_unshare_pmds(struct vm_area_struct *vma, unsigned long start, unsigned long end, bool take_locks); +static void hugetlb_unmap_range(struct mmu_gather *tlb, + struct vm_area_struct *vma, unsigned long start, + unsigned long end, struct folio *folio, + zap_flags_t zap_flags); static struct resv_map *vma_resv_map(struct vm_area_struct *vma); static inline bool subpool_is_free(struct hugepage_subpool *spool) @@ -5227,6 +5231,8 @@ unsigned long move_hugetlb_page_tables(struct vm_area_struct *vma, for (; old_addr < old_end; old_addr += sz, new_addr += sz) { const unsigned long offset_to_last_entry = (old_addr | last_addr_mask) - old_addr; + const unsigned long offset_to_last_dst_entry = + (new_addr | last_addr_mask) - new_addr; src_pte = hugetlb_walk(vma, old_addr, sz); if (!src_pte) { @@ -5243,6 +5249,24 @@ unsigned long move_hugetlb_page_tables(struct vm_area_struct *vma, continue; } + /* + * Avoid entering the destination PMD sharing path while holding + * i_mmap_rwsem for write. Leave destination page table + * population to the fault path, which can share the PMD lazily. + */ + if (sz == PMD_SIZE && want_pmd_share(new_vma, new_addr)) { + const unsigned long unmap_size = + min(old_end - old_addr, + offset_to_last_dst_entry + sz); + + hugetlb_unmap_range(&tlb, vma, old_addr, + old_addr + unmap_size, NULL, + ZAP_FLAG_DROP_MARKER); + old_addr += unmap_size - sz; + new_addr += unmap_size - sz; + continue; + } + dst_pte = huge_pte_alloc(mm, new_vma, new_addr, sz); if (!dst_pte) break; @@ -5262,9 +5286,10 @@ unsigned long move_hugetlb_page_tables(struct vm_area_struct *vma, return len + old_addr - old_end; } -void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, - unsigned long start, unsigned long end, - struct folio *folio, zap_flags_t zap_flags) +static void hugetlb_unmap_range(struct mmu_gather *tlb, + struct vm_area_struct *vma, unsigned long start, + unsigned long end, struct folio *folio, + zap_flags_t zap_flags) { struct mm_struct *mm = vma->vm_mm; const bool folio_provided = !!folio; @@ -5282,13 +5307,6 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, BUG_ON(start & ~huge_page_mask(h)); BUG_ON(end & ~huge_page_mask(h)); - /* - * This is a hugetlb vma, all the pte entries should point - * to huge page. - */ - tlb_change_page_size(tlb, sz); - tlb_start_vma(tlb, vma); - last_addr_mask = hugetlb_mask_last_page(h); address = start; for (; address < end; address += sz) { @@ -5417,6 +5435,15 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, if (folio_provided) break; } +} + +void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, + unsigned long start, unsigned long end, + struct folio *folio, zap_flags_t zap_flags) +{ + tlb_change_page_size(tlb, huge_page_size(hstate_vma(vma))); + tlb_start_vma(tlb, vma); + hugetlb_unmap_range(tlb, vma, start, end, folio, zap_flags); tlb_end_vma(tlb, vma); huge_pmd_unshare_flush(tlb, vma); -- 2.53.0