From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A63BA27C162 for ; Sat, 10 Oct 2026 20:45:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791665158; cv=none; b=ey6L1DqP0/XI7wZhlqNmP1lkdHBZdeUdi9+Rtf6McHBFcTo6N+JWtgceXk/QGPaCg4MTlBo5oYjOOF1FuOQmh52sow7h55PSXOsv5TIk2hQU/eG3YhiiCwaSBSDn1sZUNDaH/3RwCB9SdFJzVLl7jwhX1Lv8rOK1f+kTElSoz8w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791665158; c=relaxed/simple; bh=bHb+2UAy/qq3qUdtk8xs8GxLloD+QE3LANm1WIjlVyU=; h=Date:To:From:Subject:Message-Id; b=SrBT3MZli3uoePdYQUnjINP989yU+ZNqmvxL7eMhi3r/WohNdFYXnTZrWHy2fnpKHilXBdiLY2Tg3uFKJD8jsoNKjEzNYNJ5L+Sk0sfd7ZNp0GLUfjsi9ZlaNaxZZzv5u9PNH614W/Ki43nLX7tXxp+bh1JSJzLIaGxwgdWS9BA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=k8DRrsdv; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="k8DRrsdv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3283C1F00893; Sat, 10 Oct 2026 20:45:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1791665157; bh=jsM7RqD9t1xaBUVfo/Tcb5nJHKHsoXgVoca+i0L1Ytk=; h=Date:To:From:Subject; b=k8DRrsdvVulTMgUtMhAeM2Vc42XjaaiZsgPYVL3r+OdSIghIkQhTQUdjDlWfP6ccJ WTgvC5hS1mBwI+31Ng27J8FqQxcNkSryr2kAB3FEB/p1BjwU0cqq2zjv4MvjpRnLaK /xuZjPhOtHSctYKH0jaGFye/z8nYYZV4UxUpMlA8= Date: Sat, 10 Oct 2026 13:45:56 -0700 To: mm-commits@vger.kernel.org,vbabka@kernel.org,surenb@google.com,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: <20261010204557.3283C1F00893@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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: Sat, 10 Oct 2026 15:22:18 +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 add smp_wmb()/smp_rmb() memory barriers, 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(). Link: https://lore.kernel.org/542c97482eae84f86704bcee56482633d1b32321.1791616645.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/ Cc: David Hildenbrand Cc: Lorenzo Stoakes Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Qi Zheng Cc: Jan Kara Cc: Pedro Falcato --- mm/memory.c | 29 ++++++++++++++++++++--------- 1 file changed, 20 insertions(+), 9 deletions(-) --- 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. * @@ -2081,16 +2090,13 @@ retry: * to ensure they are still none, thereby preventing the pte entries * from being repopulated by another thread. */ - if (can_reclaim_pt && direct_reclaim && addr == end) + if (can_reclaim_pt && direct_reclaim && addr == end) { + /* + * The rmap changes need to be observed before PTEs get zapped. + * Pairs with smp_rmb() in zap_pmd_range(). + */ + smp_wmb(); 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); @@ -2145,6 +2151,11 @@ static inline unsigned long zap_pmd_rang sync_with_folio_pmd_zap(tlb->mm, pmd); } if (pmd_none(*pmd)) { + /* + * Order this PMD read before the folio's mapcount read. + * Pairs with smp_wmb() in zap_pte_range(). + */ + smp_rmb(); 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