From: Liam R. Howlett Liam.Howlett@oracle.com
commit 6db504ce55bdbc575723938fc480713c9183f6a2 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/ksm.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
--- a/mm/ksm.c +++ b/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);