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=1793070762; b=tjlyBGYG1oNf3fxo13UR3Jf/6DWC7biWqm/TGhiyoOhmVcMAtwcfzKnzEFpxSCyGuBBG BtOyKfiU7MvCn/0B9Wk3Vg1LBzFEAUedJUjg11unWMrSFp7kFueZSkTKS/0CjLV/4sw1E B0/SHpXBnx4r5tHWZtqIc0SMTiM9Y87yQ8/I0cT8RkHxkygdIVXUeKyXMylxfLGUxmihs qzFr6Wwd++Xfv/DIViZG3j6D0ChslCC6VEWDp5dI3YpiCDH+uTT9NZwcyWVakTJV+QX22 Yf2PD/UL5ZxKDlSQwR+Yph0spmMCWeJhbcSmSsNb6Y5eEoV/Bc6ePzvfyJOmB7Dz3XA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793070762; h=Received:DKIM-Signature:Date:To:From:Subject:Message-Id; bh=1H55sXRl8fBNx4ZcP0zjSnu9yMIGqAGD9i4GTFf9CNg=; b=Kd4DxYIL5BTZPVWg6vIQ5KUdXEWBs382snvr72HJIjQQ3VBbKREht8QT5Bxlxp9qh6eA HShYndxzNBTxEFaDI9ZpEeK6ce+ibHIdIvYdtghtKWmSEk7sdPizWpq/62WMLQlbzKonN 9dVzbUVS74/hdToAW2EMcUI86L1Hb2E0i64OPXulrS012xx4LuFRsmcE7LM5jMT1iQ1Yy HX2M6O7RsfRVUyX9nynDGq4YwOlI+N7/b7VriVHn/qT0OHBOgJ7gtWdki5jiouJf1mT12 DB+SyhUec4AerP696zEe9obvZbQ9ldEyH3NmOLqA3304HE7kZap/3oCVAgqyZaQ/83w== 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=WCNGmpTl; 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 47CAF606A31A for ; Tue, 27 Oct 2026 03:12:42 +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=WCNGmpTl Received: by smtp.kernel.org (Postfix) with ESMTPSA id B5EE51F01825; Tue, 27 Oct 2026 03:12:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1793070761; bh=1H55sXRl8fBNx4ZcP0zjSnu9yMIGqAGD9i4GTFf9CNg=; h=Date:To:From:Subject; b=WCNGmpTlrzp1Z81zXIfASeWq+6l/JD2yOqysOwpaKz1B8Bq5V/k1YfaJL2CEtHSqD FDLE4OpgBDcslvigkotMLWx2zr9Rfp/lmLjja7fN/FIP2ugE8sEsGAq401/Rrn5jYX EvVPTFAb+1A7XUqRCgx2K9v+ioRvke4hx+JexOU4= Date: Mon, 26 Oct 2026 20:12:41 -0700 To: mm-commits@vger.kernel.org,baolin.wang@linux.alibaba.com, akpm@linux-foundation.org From: Andrew Morton Subject: [to-be-updated] mm-memory-fix-truncation-removing-mapped-folios.patch removed from -mm tree Message-Id: <20261027031241.B5EE51F01825@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 quilt patch titled Subject: mm: memory: fix truncation removing mapped folios has been removed from the -mm tree. Its filename was mm-memory-fix-truncation-removing-mapped-folios.patch This patch was dropped because an updated version will be issued ------------------------------------------------------ From: Baolin Wang Subject: mm: memory: fix truncation removing mapped folios Date: Mon, 26 Oct 2026 10:05:06 +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(). Link: https://lore.kernel.org/4cc521a118564b4145edf0324066ab532fb41181.1792979870.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 --- mm/internal.h | 10 ++++++---- mm/memory.c | 28 +++++++++++++++------------- 2 files changed, 21 insertions(+), 17 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); /* @@ -2139,12 +2142,11 @@ static inline unsigned long zap_pmd_rang 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)) { + 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