On Tue, Jan 15, 2019 at 10:13:00AM -0800, Davidlohr Bueso wrote:
> ib_umem_get() uses gup_longterm() and relies on the lock to
> stabilze the vma_list, so we cannot really get rid of mmap_sem
> altogether, but now that the counter is atomic, we can get of
> some complexity that mmap_sem brings with only pinned_vm.
>
> Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
> drivers/infiniband/core/umem.c | 41 ++---------------------------------------
> 1 file changed, 2 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> index bf556215aa7e..baa2412bf6fb 100644
> +++ b/drivers/infiniband/core/umem.c
> @@ -160,15 +160,12 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
>
> lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>
> - down_write(&mm->mmap_sem);
> - new_pinned = atomic_long_read(&mm->pinned_vm) + npages;
> + new_pinned = atomic_long_add_return(npages, &mm->pinned_vm);
> if (new_pinned > lock_limit && !capable(CAP_IPC_LOCK)) {
I thought a patch had been made for this to use check_overflow...
npages is controlled by userspace, so can we protect pinned_vm from
overflow in some way that still allows it to be atomic?
Jason
