On Sat, 31 Jul 2021 10:53:41 -0700 Luigi Rizzo <lrizzo@xxxxxxxxxx> wrote: > find_vma() and variants need protection when used. > This patch adds mmap_assert_lock() calls in the functions. > > To make sure the invariant is satisfied, we also need to add a > mmap_read_loc() around the get_user_pages_remote() call in > get_arg_page(). The lock is not strictly necessary because the mm > has been newly created, but the extra cost is limited because > the same mutex was also acquired shortly before in __bprm_mm_init(), > so it is hot and uncontended. > Well, it isn't cost-free. find_vma() is called a lot and a surprising number of systems apparently run with CONFIG_DEBUG_VM. Why do you think this cost is justified?
