[PATCH v2 27/33] mm: prevent userfaults to be handled under per-vma lock
From: Suren Baghdasaryan <surenb@google.com>
Date: 2023-01-27 19:45:35
Also in:
linux-arm-kernel, linux-mm, lkml
Subsystem:
memory management, memory management - core, the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
Due to the possibility of handle_userfault dropping mmap_lock, avoid fault handling under VMA lock and retry holding mmap_lock. This can be handled more gracefully in the future. Signed-off-by: Suren Baghdasaryan <surenb@google.com> Suggested-by: Peter Xu <peterx@redhat.com> --- mm/memory.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/mm/memory.c b/mm/memory.c
index 33ecc850d3cb..55582c6fa2fd 100644
--- a/mm/memory.c
+++ b/mm/memory.c@@ -5256,6 +5256,15 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, if (!vma_start_read(vma)) goto inval; + /* + * Due to the possibility of userfault handler dropping mmap_lock, avoid + * it for now and fall back to page fault handling under mmap_lock. + */ + if (userfaultfd_armed(vma)) { + vma_end_read(vma); + goto inval; + } + /* Check since vm_start/vm_end might change before we lock the VMA */ if (unlikely(address < vma->vm_start || address >= vma->vm_end)) { vma_end_read(vma);
--
2.39.1