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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 00721157ae682-79a903e0b8csm54549467b3.12.2026.03.23.02.34.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Mar 2026 02:34:21 -0700 (PDT) Date: Mon, 23 Mar 2026 02:34:19 -0700 (PDT) From: Hugh Dickins To: Greg Kroah-Hartman cc: Hugh Dickins , Andrew Morton , Baolin Wang , Baoquan He , Barry Song , Chris Li , David Hildenbrand , Dev Jain , Greg Thelen , Guenter Roeck , Kairui Song , Kemeng Shi , Lance Yang , Matthew Wilcox , Nhat Pham , linux-mm@kvack.org, stable@vger.kernel.org Subject: [PATCH 6.12.y 1/4] mm: shmem: fix potential data corruption during shmem swapin In-Reply-To: Message-ID: <0e918493-29b1-de47-9fca-b1fa93156d63@google.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Stat-Signature: 86embfj8ia4j7ec9z8geb8hynye3wfmx X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: BBC7F12000F X-HE-Tag: 1774258463-344681 X-HE-Meta: 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 DDhVX0Bm 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Baolin Wang commit 058313515d5aab10d0a01dd634f92ed4a4e71d4c upstream. Alex and Kairui reported some issues (system hang or data corruption) when swapping out or swapping in large shmem folios. This is especially easy to reproduce when the tmpfs is mount with the 'huge=within_size' parameter. Thanks to Kairui's reproducer, the issue can be easily replicated. The root cause of the problem is that swap readahead may asynchronously swap in order 0 folios into the swap cache, while the shmem mapping can still store large swap entries. Then an order 0 folio is inserted into the shmem mapping without splitting the large swap entry, which overwrites the original large swap entry, leading to data corruption. When getting a folio from the swap cache, we should split the large swap entry stored in the shmem mapping if the orders do not match, to fix this issue. Link: https://lkml.kernel.org/r/2fe47c557e74e9df5fe2437ccdc6c9115fa1bf70.1740476943.git.baolin.wang@linux.alibaba.com Fixes: 809bc86517cc ("mm: shmem: support large folio swap out") Signed-off-by: Baolin Wang Reported-by: Alex Xu (Hello71) Reported-by: Kairui Song Closes: https://lore.kernel.org/all/1738717785.im3r5g2vxc.none@localhost/ Tested-by: Kairui Song Cc: David Hildenbrand Cc: Lance Yang Cc: Matthew Wilcow Cc: Hugh Dickins Cc: Signed-off-by: Andrew Morton [ hughd: removed skip_swapcache dependencies ] Signed-off-by: Hugh Dickins --- mm/shmem.c | 30 +++++++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index 5e8184821fac..9105c732f341 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2132,7 +2132,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, struct swap_info_struct *si; struct folio *folio = NULL; swp_entry_t swap; - int error, nr_pages; + int error, nr_pages, order, split_order; VM_BUG_ON(!*foliop || !xa_is_value(*foliop)); swap = radix_to_swp_entry(*foliop); @@ -2151,8 +2151,8 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, /* Look it up and read it in.. */ folio = swap_cache_get_folio(swap, NULL, 0); + order = xa_get_order(&mapping->i_pages, index); if (!folio) { - int split_order; /* Or update major stats only when swapin succeeds?? */ if (fault_type) { @@ -2189,13 +2189,37 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, error = -ENOMEM; goto failed; } + } else if (order != folio_order(folio)) { + /* + * Swap readahead may swap in order 0 folios into swapcache + * asynchronously, while the shmem mapping can still stores + * large swap entries. In such cases, we should split the + * large swap entry to prevent possible data corruption. + */ + split_order = shmem_split_large_entry(inode, index, swap, gfp); + if (split_order < 0) { + error = split_order; + goto failed; + } + + /* + * If the large swap entry has already been split, it is + * necessary to recalculate the new swap entry based on + * the old order alignment. + */ + if (split_order > 0) { + pgoff_t offset = index - round_down(index, 1 << split_order); + + swap = swp_entry(swp_type(swap), swp_offset(swap) + offset); + } } /* We have to do this with folio locked to prevent races */ folio_lock(folio); if (!folio_test_swapcache(folio) || folio->swap.val != swap.val || - !shmem_confirm_swap(mapping, index, swap)) { + !shmem_confirm_swap(mapping, index, swap) || + xa_get_order(&mapping->i_pages, index) != folio_order(folio)) { error = -EEXIST; goto unlock; }