The patch titled Subject: mm/ksm: fix race with VMA iteration and mm_struct teardown has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-ksm-fix-race-with-vma-iteration-and-mm_struct-teardown.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: "Liam R. Howlett" Liam.Howlett@oracle.com Subject: mm/ksm: fix race with VMA iteration and mm_struct teardown Date: Wed, 8 Mar 2023 17:03:10 -0500

exit_mmap() will tear down the VMAs and maple tree with the mmap_lock held in write mode. Ensure that the maple tree is still valid by checking ksm_test_exit() after taking the mmap_lock in read mode, but before the for_each_vma() iterator dereferences a destroyed maple tree.

Since the maple tree is destroyed, the flags telling lockdep to check an external lock has been cleared. Skip the for_each_vma() iterator to avoid dereferencing a maple tree without the external lock flag, which would create a lockdep warning.

Link: https://lkml.kernel.org/r/20230308220310.3119196-1-Liam.Howlett@oracle.com Fixes: a5f18ba07276 ("mm/ksm: use vma iterators instead of vma linked list") Signed-off-by: Liam R. Howlett Liam.Howlett@oracle.com Reported-by: Pengfei Xu pengfei.xu@intel.com Link: https://lore.kernel.org/lkml/ZAdUUhSbaa6fHS36@xpf.sh.intel.com/ Reported-by: syzbot+2ee18845e89ae76342c5@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?id=64a3e95957cd3deab99df7cd7b5a9475af92c93... Acked-by: David Hildenbrand david@redhat.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: heng.su@intel.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

--- a/mm/ksm.c~mm-ksm-fix-race-with-vma-iteration-and-mm_struct-teardown +++ a/mm/ksm.c @@ -988,9 +988,15 @@ static int unmerge_and_remove_all_rmap_i

mm = mm_slot->slot.mm; mmap_read_lock(mm); + + /* + * Exit right away if mm is exiting to avoid lockdep issue in + * the maple tree + */ + if (ksm_test_exit(mm)) + goto mm_exiting; + for_each_vma(vmi, vma) { - if (ksm_test_exit(mm)) - break; if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) continue; err = unmerge_ksm_pages(vma, @@ -999,6 +1005,7 @@ static int unmerge_and_remove_all_rmap_i goto error; }

+mm_exiting: remove_trailing_rmap_items(&mm_slot->rmap_list); mmap_read_unlock(mm);

_

Patches currently in -mm which might be from Liam.Howlett@oracle.com are

maple_tree-fix-mas_skip_node-end-slot-detection.patch test_maple_tree-add-more-testing-for-mas_empty_area.patch mm-ksm-fix-race-with-vma-iteration-and-mm_struct-teardown.patch maple_tree-be-more-cautious-about-dead-nodes.patch maple_tree-detect-dead-nodes-in-mas_start.patch maple_tree-fix-freeing-of-nodes-in-rcu-mode.patch maple_tree-remove-extra-smp_wmb-from-mas_dead_leaves.patch maple_tree-fix-write-memory-barrier-of-nodes-once-dead-for-rcu-mode.patch maple_tree-add-smp_rmb-to-dead-node-detection.patch maple_tree-add-rcu-lock-checking-to-rcu-callback-functions.patch mm-enable-maple-tree-rcu-mode-by-default.patch