The patch below does not apply to the 6.13-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.13.y git checkout FETCH_HEAD git cherry-pick -x 058313515d5aab10d0a01dd634f92ed4a4e71d4c # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025030953-alkalize-eardrum-de40@gregkh' --subject-prefix 'PATCH 6.13.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 058313515d5aab10d0a01dd634f92ed4a4e71d4c Mon Sep 17 00:00:00 2001 From: Baolin Wang baolin.wang@linux.alibaba.com Date: Tue, 25 Feb 2025 17:52:55 +0800 Subject: [PATCH] mm: shmem: fix potential data corruption during shmem swapin
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/2fe47c557e74e9df5fe2437ccdc6c9115fa1bf70.174047694... Fixes: 809bc86517cc ("mm: shmem: support large folio swap out") Signed-off-by: Baolin Wang baolin.wang@linux.alibaba.com Reported-by: Alex Xu (Hello71) alex_y_xu@yahoo.ca Reported-by: Kairui Song ryncsn@gmail.com Closes: https://lore.kernel.org/all/1738717785.im3r5g2vxc.none@localhost/ Tested-by: Kairui Song kasong@tencent.com Cc: David Hildenbrand david@redhat.com Cc: Lance Yang ioworker0@gmail.com Cc: Matthew Wilcow willy@infradead.org Cc: Hugh Dickins hughd@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org
diff --git a/mm/shmem.c b/mm/shmem.c index 4ea6109a8043..cebbac97a221 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2253,7 +2253,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, struct folio *folio = NULL; bool skip_swapcache = false; 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); @@ -2272,10 +2272,9 @@ 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 order = xa_get_order(&mapping->i_pages, index); bool fallback_order0 = false; - int split_order;
/* Or update major stats only when swapin succeeds?? */ if (fault_type) { @@ -2339,6 +2338,29 @@ 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); + } }
alloced: @@ -2346,7 +2368,8 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, folio_lock(folio); if ((!skip_swapcache && !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; }