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Received: from localhost(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XCT5qzQ_1791540731 cluster:ay36) by smtp.aliyun-inc.com; Fri, 09 Oct 2026 18:12:11 +0800 From: Baolin Wang To: akpm@linux-foundation.org, david@kernel.org Cc: ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, qi.zheng@linux.dev, jack@suse.cz, pfalcato@suse.de, ayushr@modal.com, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] mm: memory: fix truncation removing mapped folios Date: Fri, 9 Oct 2026 18:12:03 +0800 Message-ID: <0d2a1809fa1cfc22ad3df26ec28b2d30e5cdf3bd.1791540483.git.baolin.wang@linux.alibaba.com> X-Mailer: git-send-email 2.43.5 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: C052C20005 X-Rspam-User: X-Stat-Signature: n8mw33ag86ycppx7dexbwoo3ct3k7zt6 X-HE-Tag: 1791540735-279518 X-HE-Meta: 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 +pLrKSBI vwFDm39Jiltzo6ks5K9p90nmUoMu5+8pfrN3Bs7bAsRIxt9zgrpaFI4/uBhgkwIPZbCOHpbp1qMw7hVBG6zf09z30KbZHy0Skaf3FB0Vgg3Qbs3H2dsBHS4GFVisHyVKMdR8HKOOhnAsoIaGP97o5HMdP5+6AWBJypGlYwId7KAMAFKsiPAsBIzDGEyGLnLFzRgQMIrD29MeNmIP6LzqFXRC+l98V5OlNg7UsEhEc3sMBA9fVB7tSg/wipl2k5SzbzAEWnYt+SllemoYCoEnKAUjXBt830iVcVoWdv6PZhJH+MSYPGtfRWzGhhX6YmtpRwqf/bACnm65xlSP1gxmETlv+SA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 a smp_wmb() memory barrier, 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(). [1] https://lore.kernel.org/all/20260925065013.3682431-1-ayushr@modal.com/ Reported-by: Ayush Ranjan Closes: https://lore.kernel.org/all/20260924061708.1645968-1-ayushr@modal.com/ Fixes: 6375e95f381e ("mm: pgtable: reclaim empty PTE page in madvise(MADV_DONTNEED)") Signed-off-by: Baolin Wang --- mm/memory.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 1f5d5f7d39cd..0272217ad7b0 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2036,6 +2036,15 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, } } 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. * @@ -2044,16 +2053,10 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, * 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) { + /* rmap changes need to be observed before e.g PTEs get zapped. */ + 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); -- 2.47.3