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.

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... Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: heng.su@intel.com Cc: lkp@intel.com Cc: Stable@vger.kernel.org Fixes: a5f18ba07276 ("mm/ksm: use vma iterators instead of vma linked list") Signed-off-by: Liam R. Howlett Liam.Howlett@oracle.com Acked-by: David Hildenbrand david@redhat.com ---

Andrew,

I've included this note because I've changed the subject between v1 and v2. This is for mm-hotfixes-unstable.

Replaces: b6d4338e8dd2 ("mm/ksm: fix race with ksm_exit() in VMA iteration")

v1: https://lore.kernel.org/linux-mm/20230307205951.2465275-1-Liam.Howlett@oracl...

Changes since v1: - Commit log & subject. - Added Acked-by

mm/ksm.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c index 525c3306e78b..d6280b258ece 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1044,9 +1044,15 @@ static int unmerge_and_remove_all_rmap_items(void)

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, @@ -1055,6 +1061,7 @@ static int unmerge_and_remove_all_rmap_items(void) goto error; }

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