On 12.08.24 18:42, Jann Horn wrote:
Since khugepaged was changed to allow retracting page tables in file mappings without holding the mmap lock, these BUG_ON()s are wrong - get rid of them.
We could also remove the preceding "if (unlikely(...))" block, but then we could reach pte_offset_map_lock() with transhuge pages not just for file mappings but also for anonymous mappings - which would probably be fine but I think is not necessarily expected.
Cc: stable@vger.kernel.org Fixes: 1d65b771bc08 ("mm/khugepaged: retract_page_tables() without mmap or vma lock") Signed-off-by: Jann Horn jannh@google.com
mm/userfaultfd.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index ec3750467aa5..0dfa97db6feb 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -806,9 +806,10 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, err = -EFAULT; break; }
BUG_ON(pmd_none(*dst_pmd));BUG_ON(pmd_trans_huge(*dst_pmd));
/** For shmem mappings, khugepaged is allowed to remove page* tables under us; pte_offset_map_lock() will deal with that.*/err = mfill_atomic_pte(dst_pmd, dst_vma, dst_addr, src_addr, flags, &folio);
Acked-by: David Hildenbrand david@redhat.com