From: Jann Horn <jannh@xxxxxxxxxx> Subject: mm/gup: assert that the mmap lock is held in __get_user_pages() After having cleaned up all GUP callers (except for the atomisp staging driver, which currently gets mmap locking completely wrong [1]) to always ensure that they hold the mmap lock when calling into GUP (unless the mm is not yet globally visible), add an assertion to make sure it stays that way going forward. [1] https://lore.kernel.org/lkml/CAG48ez3tZAb9JVhw4T5e-i=h2_DUZxfNRTDsagSRCVazNXx5qA@xxxxxxxxxxxxxx/ Link: https://lkml.kernel.org/r/CAG48ez1GM==OnHpS=ghqZNJPn02FCDUEHc7GQmGRMXUD_aKudg@xxxxxxxxxxxxxx Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Acked-by: Michel Lespinasse <walken@xxxxxxxxxx> Cc: "Eric W . Biederman" <ebiederm@xxxxxxxxxxxx> Cc: John Hubbard <jhubbard@xxxxxxxxxx> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/gup.c | 2 ++ 1 file changed, 2 insertions(+) --- a/mm/gup.c~mm-gup-assert-that-the-mmap-lock-is-held-in-__get_user_pages +++ a/mm/gup.c @@ -1027,6 +1027,8 @@ static long __get_user_pages(struct mm_s struct vm_area_struct *vma = NULL; struct follow_page_context ctx = { NULL }; + mmap_assert_locked(mm); + if (!nr_pages) return 0; _
