From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=115.124.30.119 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793148787; b=NxEJvYEi1AJlvyoJfhkYdBw0Kk925ZSh7o/o6u+BuNJrni7rEkkZOqvshRpnsxemBLXY u7CuSvS6CSiK36XhG2ACco2ClmvZhZjQAtlxwYhDOzkZ4fCdcdgRLLjz+rW9Qcn9pkphP m2nNF4G+KPhsd7vjcu8lwqZky2WroPMJdMeORNL0Ow5gpKbMVOA7+uz3qKL3Jl0d6adit PtK8fLebjZXuorLJncUNynu3zwq/yvvYOQ7TA7WdhkalJMBG6UPkjx3IX+HMJuHva39tP c3i7pN5OCe55nhKbjPumg5P7JpL/XcxweD1dsOkrkz7GQpP32b/ES0G3TOFUTVPDL4A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793148787; h=DMARC-Filter:DKIM-Signature:X-Alimail-AntiSpam:Received:From:To:Cc: Subject:Date:Message-ID:X-Mailer:MIME-Version: Content-Transfer-Encoding; bh=70/2LdS5pBXpfNj8kBNHr883OekoIQf/Q1qvO8XzJk4=; b=mu4yxTr95u3og6r35HMpb45gpHNv0/5MslVmTkPKLV/M0nX4f8Ueq63qiQ/fsiw4/9Oq 5Y0euxIM++dClwq3R5v1sxAVt+Hka4pBJkkFAJ90pYX1D6BKLUKyNOYntn6iGJ0vITcu5 SEnU/sS6N9/FRU/ASDus69yLXJIavZHVF4vZUUM4qRucJ432PKvZ0Z2j4M+RT9OgkC2ax I8z8IK32UzomossH9U49zUQgVl0TCfOAbW8On0a9XzRbOyfY6BYRp1ts0CDH3Ib1avdGv 7/ksP7FST/lbClrvuLr4RlEecFsmxv0BOoIFqu05GrUhto8j8aZ5ICXz6n/M2/fkD8A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass header.d=linux.alibaba.com header.i=@linux.alibaba.com header.a=rsa-sha256 header.s=default header.b=dOTcvjMh; arc=none smtp.remote-ip=115.124.30.119 Received: from out30-119.freemail.mail.aliyun.com (out30-119.freemail.mail.aliyun.com [115.124.30.119]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C3886606A31A for ; Wed, 28 Oct 2026 00:53:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org C3886606A31A Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.a=rsa-sha256 header.s=default header.b=dOTcvjMh DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1793148783; h=From:To:Subject:Date:Message-ID:MIME-Version; bh=70/2LdS5pBXpfNj8kBNHr883OekoIQf/Q1qvO8XzJk4=; b=dOTcvjMhIMZtReERq5BBmSvPLIse/JvdeAMgqwfIAWojRzaV+JIxNxbyQh+cZa4TtQmG9T0K1fAYolH2LZkN656iwot3Py//wkENFFMC5takVL6G1PeRYzS2Z0jRWI+5gMBkY0rk+osxqLZGehj5pdI72CxYxe39T5VOL6Z/J44= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R111e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045133197;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=15;SR=0;TI=SMTPD_---0XDf2cRu_1793148781; Received: from localhost(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XDf2cRu_1793148781 cluster:ay36) by smtp.aliyun-inc.com; Wed, 28 Oct 2026 08:53:01 +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 v6] mm: memory: fix truncation removing mapped folios Date: Wed, 28 Oct 2026 08:52:57 +0800 Message-ID: <14ebbd556cc4941f0ebc43da59fa6a2fdca25dc8.1793148609.git.baolin.wang@linux.alibaba.com> X-Mailer: git-send-email 2.43.5 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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. [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)") Cc: stable@vger.kernel.org Acked-by: Qi Zheng Reviewed-by: Pedro Falcato Reviewed-by: Lorenzo Stoakes (ARM) Signed-off-by: Baolin Wang --- Andrew, sorry for the trouble caused by the several iterations:). Changes from v5: - Keep the 2nd pmd_none() check (per David). - Add Cc: stable (per Andrew). Changes from v4: - Put the pmd_none() check in the 'else if' branch (per David). Changes from v3: - Collect review tags from Qi, Pedro and Lorenzo. Thanks. - Update the related comments per Lorenzo. Changes from v2: - Use use sync_with_folio_pmd_zap() to sync with concurrent zapping (Per David). Changes from v1: - Add an smp_rmb() to pair with the smp_wmb() (Per Lorenzo and Pedro). --- mm/internal.h | 10 ++++++---- mm/memory.c | 35 ++++++++++++++++++++--------------- 2 files changed, 26 insertions(+), 19 deletions(-) diff --git a/mm/internal.h b/mm/internal.h index b1b0f29d2216..ffb8eaec90e3 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -584,14 +584,16 @@ void free_pgtables(struct mmu_gather *tlb, struct unmap_desc *desc); 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. */ diff --git a/mm/memory.c b/mm/memory.c index e911e63ba1ed..e0fef107a022 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. * @@ -2043,18 +2052,12 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, * 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); /* @@ -2101,13 +2104,15 @@ static inline unsigned long zap_pmd_range(struct mmu_gather *tlb, 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; } -- 2.47.3