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=1793154464; b=psuqvxVR6rPp+P0MgQNpMBt0AYSgVBX5gum45QlHc9Y6SPExJS9YJXRTZmaWnohrlULI 1L0OJGGOOKfgW3C/jU3svAm9qGq16Gpet7WqLXvtem45UTM5/EhNuUCbYDjOxDKHTgcWg F0OpqkoHdW3IUKYee5YbLJ6+721MKJ+Gawpt/c8FP43yfcZrPqlpjDigHJwrzmRbFLfnp kN+ruioGayMXvNaosaj8YdxpkQ9+uZ2PSDlFcNKPStj/CBSwdrYFCwkmG8eORRhBDOpF0 1DBN7ekxM7jmQBy+1r3X22rUoVRNkH5sV4fe8mJ6FRczLKNXV/KlLGpLOmnY4HM1TJQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793154464; h=Received:DKIM-Signature:Date:To:From:Subject:Message-Id; bh=f2V+QhR3ouV+4TSh8wb5W05ywr0Fs0XryAtmuVyoRSs=; b=NE5j7pJufGOJ3KQIKz+N4+icFBp37GjBrpMEJzr+XB5mmfJugT+invM7xm5wjw31ESQ0 r5iCcXougVHdQyH3hYSXEA4cNYz7kDbwmO3eTDwodQiTfixR9r88W2WELEnMT+QKj97jQ dKqlOfaL2nLfNsRMUMUjxdPdWIfF/GsUpuGgGFVEtqI6O4/TvJbJZLAzl2lOYUTWqM6mv GGWnF9Yr3gVf2k7zBf91+wK8IKiNjy55+NKLeZB1bad7atKjs13BinWaJm/bsMQAlu0Ku YknzEp8710RAJw5vv9dxM4op6G/nTWxU61XEHUJvujv+jGNGSU/43OEfdMWyLAKWnyA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=0A9OvlS+; 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 5BB15606A31F; Wed, 28 Oct 2026 02:27:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=0A9OvlS+ Received: by smtp.kernel.org (Postfix) with ESMTPSA id E70C81F01829; Wed, 28 Oct 2026 02:27:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1793154464; bh=f2V+QhR3ouV+4TSh8wb5W05ywr0Fs0XryAtmuVyoRSs=; h=Date:To:From:Subject; b=0A9OvlS+JxUiHBPb9vXDTpKpWxq+0VQIhsQ38B9S6k/Ryna4tGQAUaRpf/KdiPqWY C+vfuVXJfxvJuuJ5mGyroM0jBH4oFUSNgZL3pJ3gS/gORarho/V4c7cDOqdz3sfHS1 pdFy8mLf1TYsnJxjXoZlxq2hEMYyo3IH+aI2pwaQ= Date: Tue, 27 Oct 2026 19:27:43 -0700 To: mm-commits@vger.kernel.org,vbabka@kernel.org,surenb@google.com, stable@vger.kernel.org,rppt@kernel.org,qi.zheng@linux.dev,pfalcato@suse.de, mhocko@suse.com,ljs@kernel.org,liam@infradead.org,jack@suse.cz, david@kernel.org,ayushr@modal.com,baolin.wang@linux.alibaba.com, akpm@linux-foundation.org From: Andrew Morton Subject: + mm-memory-fix-truncation-removing-mapped-folios.patch added to mm-hotfixes-unstable branch Message-Id: <20261028022743.E70C81F01829@smtp.kernel.org> X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list The patch titled Subject: mm: memory: fix truncation removing mapped folios has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-memory-fix-truncation-removing-mapped-folios.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memory-fix-truncation-removing-mapped-folios.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Baolin Wang Subject: mm: memory: fix truncation removing mapped folios Date: Wed, 28 Oct 2026 08:52:57 +0800 Ayush reported an issue that shmem/tmpfs folios are still mapped when truncating them on production: " BUG: Bad page cache in process ... pfn:... page dumped because: still mapped when deleted " I reproduced the issue with Ayush's reproducer [1] with the latest mm-unstable branch, and I got the following crash info. From the dump message, we can see that truncate_inode_folio() is really trying to remove mapped folios, which is incorrect. " [ 189.171977] page: refcount:3 mapcount:1 mapping:00000000fe168ee1 index:0x3880 pfn:0x191647 [ 189.171995] memcg:ffff0000cc073d40 [ 189.171997] aops:shmem_aops ino:3c01 dentry name(?):"memfd:runsc-memory" [ 189.172006] flags: 0x17fffef0002022d(locked|referenced|uptodate|lru| workingset|swapbacked|node=0|zone=2|lastcpupid=0x3ffff) ....... [ 189.172017] page dumped because: VM_BUG_ON_FOLIO(folio_mapped(folio)) [ 189.172026] ------------[ cut here ]------------ [ 189.172027] kernel BUG at mm/filemap.c:155! [ 189.172057] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP ....... [ 189.177721] CPU: 3 UID: 0 PID: 5521 Comm: repro Kdump: loaded Tainted: 7.3.0-rc4+ #277 PREEMPT(lazy) ....... [ 189.183986] Call trace: [ 189.184124] filemap_unaccount_folio+0xf0/0x1e8 (P) [ 189.184391] __filemap_remove_folio+0x34/0x160 [ 189.184633] filemap_remove_folio+0x4c/0xb0 [ 189.184859] truncate_inode_folio+0x34/0x58 [ 189.185087] shmem_undo_range+0x220/0x658 [ 189.185308] shmem_fallocate+0x2f0/0x470 [ 189.185527] vfs_fallocate+0x128/0x328 ...... [ 189.187078] el0t_64_sync+0x184/0x188 " After analysis, I believe the race exists between truncation and MADV_DONTNEED, and shmem's ->map_pages() merely makes the issue easier to reproduce. Since MADV_DONTNEED synchronously releases the pagetable page before calling tlb_flush_rmaps(), this could cause another thread's truncation to skip zap_pte_range() (due to pmd is none) but still observe the folio's mapcount as non-zero. A possible race scenario is as follows: CPU 0 CPU 1 shmem_fallocate madvise_dontneed_single_vma unmap_mapping_range ....... ...... (filemap_map_pages() remap folios) zap_pte_range truncate_inode_folio zap_empty_pte_table(pmd clear) unmap_mapping_folio ...... zap_pmd_range (saw pmd none, skip) filemap_remove_folio BUG_ON(folio_mapped) tlb_flush_rmaps(remove rmaps) To fix this issue, we should move the pmd clear operation (via zap_empty_pte_table()) to after tlb_flush_rmaps() and use sync_with_folio_pmd_zap() to sync with concurrent zapping, so that when we find a pmd_none() while unmapping a folio without holding the PTL, the folio's mappings are guaranteed to have been removed via tlb_flush_rmaps(). Meanwhile move the second pmd_none() check to where it belongs: if splitting zapped the PMD. Link: https://lore.kernel.org/14ebbd556cc4941f0ebc43da59fa6a2fdca25dc8.1793148609.git.baolin.wang@linux.alibaba.com Link: https://lore.kernel.org/all/20260925065013.3682431-1-ayushr@modal.com/ [1] Fixes: 6375e95f381e ("mm: pgtable: reclaim empty PTE page in madvise(MADV_DONTNEED)") Signed-off-by: Baolin Wang Signed-off-by: Andrew Morton Reported-by: Ayush Ranjan Closes: https://lore.kernel.org/all/20260924061708.1645968-1-ayushr@modal.com/ Acked-by: Qi Zheng Reviewed-by: Pedro Falcato Reviewed-by: Lorenzo Stoakes (ARM) Cc: David Hildenbrand Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Jan Kara Cc: --- mm/internal.h | 10 ++++++---- mm/memory.c | 35 ++++++++++++++++++++--------------- 2 files changed, 26 insertions(+), 19 deletions(-) --- a/mm/internal.h~mm-memory-fix-truncation-removing-mapped-folios +++ a/mm/internal.h @@ -584,14 +584,16 @@ void free_pgtables(struct mmu_gather *tl void pmd_install(struct mm_struct *mm, pmd_t *pmd, pgtable_t *pte); /** - * sync_with_folio_pmd_zap - sync with concurrent zapping of a folio PMD + * sync_with_folio_pmd_zap - sync with concurrent zapping of folios * @mm: The mm_struct. * @pmdp: Pointer to the pmd that was found to be pmd_none(). * * When we find a pmd_none() while unmapping a folio without holding the PTL, - * zap_huge_pmd() may have cleared the PMD but not yet modified the folio to - * indicate that it's unmapped. Skipping the PMD without synchronization could - * make folio unmapping code assume that unmapping failed. + * zap_huge_pmd() may have cleared the PMD but not yet updated the folio + * mapcount, and zap_empty_pte_table() clears the PMD only after the rmaps + * for the table have been removed, but nothing orders the pmd_none() read + * against later mapcount reads. Skipping the PMD without synchronization + * could make folio unmapping code assume that unmapping failed. * * Wait for concurrent zapping to complete by grabbing the PTL. */ --- a/mm/memory.c~mm-memory-fix-truncation-removing-mapped-folios +++ a/mm/memory.c @@ -2073,6 +2073,15 @@ retry: } } while (pte += nr, addr += PAGE_SIZE * nr, addr != end); + add_mm_rss_vec(mm, rss); + lazy_mmu_mode_disable(); + + /* Do the actual TLB flush before dropping ptl */ + if (force_flush) { + tlb_flush_mmu_tlbonly(tlb); + tlb_flush_rmaps(tlb, vma); + } + /* * Fast path: try to hold the pmd lock and unmap the PTE page. * @@ -2080,18 +2089,12 @@ retry: * to hold the pmd lock failed, then we need to recheck all pte entries * to ensure they are still none, thereby preventing the pte entries * from being repopulated by another thread. + * + * Clear the PMD after the rmaps for the table have been removed, in case + * an incorrect mapcount is observed after unmapping the folio. */ if (can_reclaim_pt && direct_reclaim && addr == end) direct_reclaim = zap_empty_pte_table(mm, pmd, ptl, &pmdval); - - add_mm_rss_vec(mm, rss); - lazy_mmu_mode_disable(); - - /* Do the actual TLB flush before dropping ptl */ - if (force_flush) { - tlb_flush_mmu_tlbonly(tlb); - tlb_flush_rmaps(tlb, vma); - } pte_unmap_unlock(start_pte, ptl); /* @@ -2138,13 +2141,15 @@ static inline unsigned long zap_pmd_rang addr = next; continue; } + /* We already synchronized with concurrent zapping. */ + if (pmd_none(*pmd)) { + addr = next; + continue; + } /* fall through */ - } else if (details && details->single_folio && - folio_test_pmd_mappable(details->single_folio) && - next - addr == HPAGE_PMD_SIZE && pmd_none(*pmd)) { - sync_with_folio_pmd_zap(tlb->mm, pmd); - } - if (pmd_none(*pmd)) { + } else if (pmd_none(*pmd)) { + if (details && details->single_folio) + sync_with_folio_pmd_zap(tlb->mm, pmd); addr = next; continue; } _ Patches currently in -mm which might be from baolin.wang@linux.alibaba.com are mm-memory-fix-truncation-removing-mapped-folios.patch