> -----Original Message-----
> From: linux-rdma-owner@xxxxxxxxxxxxxxx <linux-rdma-
> owner@xxxxxxxxxxxxxxx> On Behalf Of Doug Ledford
> Sent: Thursday, September 20, 2018 3:23 PM
> To: linux-rdma@xxxxxxxxxxxxxxx
> Cc: Doug Ledford <dledford@xxxxxxxxxx>
> Subject: [PATCH] RDMA/umem: Minor optimization
>
> Noticed while reviewing d4b4dd1b9706 ("RDMA/umem: Do not use
> current->tgid to track the mm_struct") patch. Why would we take a lock,
> adjust a protected variable, drop the lock, and *then* check the input into
> our protected variable adjustment? Then we have to take the lock again on
> our error unwind. Let's just check the input early and skip taking the locks
> needlessly if the input isn't valid.
>
> Signed-off-by: Doug Ledford <dledford@xxxxxxxxxx>
> ---
> drivers/infiniband/core/umem.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/infiniband/core/umem.c
> b/drivers/infiniband/core/umem.c index c32a3e27a896..34d7256f5ba0
> 100644
> --- a/drivers/infiniband/core/umem.c
> +++ b/drivers/infiniband/core/umem.c
> @@ -147,6 +147,10 @@ struct ib_umem *ib_umem_get(struct ib_ucontext
> *context, unsigned long addr,
> umem->hugetlb = 0;
>
> npages = ib_umem_num_pages(umem);
> + if (npages == 0 || npages > UINT_MAX) {
> + ret = -EINVAL;
> + goto out;
> + }
>
> lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>
> @@ -161,11 +165,6 @@ struct ib_umem *ib_umem_get(struct ib_ucontext
> *context, unsigned long addr,
>
> cur_base = addr & PAGE_MASK;
>
> - if (npages == 0 || npages > UINT_MAX) {
> - ret = -EINVAL;
> - goto vma;
> - }
> -
> ret = sg_alloc_table(&umem->sg_head, npages, GFP_KERNEL);
> if (ret)
> goto vma;
> --
> 2.17.1
Reviewed-by: Parav Pandit <parav@xxxxxxxxxxxx>
