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 1FE202264A9 for ; Fri, 16 Oct 2026 13:39:28 +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=1792157969; cv=none; b=QSZ4PmfeexzXaB3u4ivYK+vEovbB1y6HHS6sXub+veGnfb+TK4XpofD0PRphxvKMA7faXfAaED2CMeTfjlXQ3szZs4us+R0+oqmK0PkDIZw2ovVEL/kbqPKWGMF26DVsaChSDAfo4xJH8TizDByiPFLsDhVPxO0b1hd6q6CO86o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792157969; c=relaxed/simple; bh=e8JwRA9PXakOg9RXarihSGH18jKPa/I690uVai6Bh3E=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BXNhM1oHCPBdRBU0BmprULcudYh0dVrUPnvR8R0M/29HaEpA4/M29KdJdMXuYcN7J9XrNCOnVoXDSmIIvtwRK6Dwnp5PZCMiR5VBX4zdQOYVGfMqTxk73zGa3fI976vJT6RqR9BBWqKyKB/sKH02ikzq8qsc1V153X2ABUltjRE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=G0SLD7gC; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="G0SLD7gC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C05721F000C4; Fri, 16 Oct 2026 13:39:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792157968; bh=1mq+oT3fIIASgxSWnNBq/FHWX6ezxg9aNmqPL9hJIw4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=G0SLD7gClK6j8OhKEgGuCHXUqy4BuQU+q1ru07LCA4igjevrlMxDR7mLmD9L5Qt9g cPpyC/v2CLPOoJWMc5QkEQsOWkhlLGEKRUIv/yYYQJYPBVIq+V2NfOEBiucC6hQZOr /Z/iebLFRatS0fVGKc1/Sd7jZO6P4JvIJshqmjxZEREcHnCy7QEoubV+BYzsqAKgBV APUEbBPOeUSDBbLcD1iQUKFTUGQP6W72UGF4R8vdxu4zATwyy9p8NdCFsl3mnAVhMW tvdFqdr18Abh74/QiyUeXFJWwxluhmJiK1YKj2WzoSybkTBv9L3JPWFSkMT2KNSLxS +Z8WXtO9uhIBg== Message-ID: <094c9af9-3ade-420d-87d1-976730a5079a@kernel.org> Date: Fri, 16 Oct 2026 11:30:09 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm: memory: fix truncation removing mapped folios To: Baolin Wang , akpm@linux-foundation.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, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/16/26 03:48, Baolin Wang wrote: > 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(). > > [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 > --- > 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 | 9 +++++---- > mm/memory.c | 25 ++++++++++++------------- > 2 files changed, 17 insertions(+), 17 deletions(-) > > diff --git a/mm/internal.h b/mm/internal.h > index 0434dfcfc36f..6d8f494296a4 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -585,14 +585,15 @@ 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() or zap_empty_pte_table() may have cleared the PMD but not > + * yet modified the mapped folios to indicate they are unmapped. 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 6a8e7772b8d6..8f7ba427371b 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. > * > @@ -2046,15 +2055,6 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, > */ > 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); > > /* > @@ -2102,12 +2102,11 @@ static inline unsigned long zap_pmd_range(struct mmu_gather *tlb, > 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; By keeping it in the else path above you avoid re-taking the lock if you just sync'ed already when you saw pte_present() and resulted in pte_none(). -- Cheers, David