Re: [RFC PATCH v2 1/7] IB/mlx5: Change ib_umem_odp_map_dma_single_page() to retain umem_mutex

lizhijian
2022-11-17T13:20:57Z

On 11/11/2022 17:22, Daisuke Matsuda wrote:
> ib_umem_odp_map_dma_single_page(), which has been used only by the mlx5
> driver, holds umem_mutex on success and releases on failure. This
> behavior is not convenient for other drivers to use it, so change it to
> always retain mutex on return.
>
> Signed-off-by: Daisuke Matsuda <matsuda-daisuke@fujitsu.com>
> ---
> drivers/infiniband/core/umem_odp.c | 8 +++-----
> drivers/infiniband/hw/mlx5/odp.c | 4 +++-
> 2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
> index e9fa22d31c23..49da6735f7c8 100644
> --- a/drivers/infiniband/core/umem_odp.c
> +++ b/drivers/infiniband/core/umem_odp.c
> @@ -328,8 +328,8 @@ static int ib_umem_odp_map_dma_single_page(
> *
> * Maps the range passed in the argument to DMA addresses.
> * The DMA addresses of the mapped pages is updated in umem_odp->dma_list.
> - * Upon success the ODP MR will be locked to let caller complete its device
> - * page table update.
> + * The umem mutex is locked in this function. Callers are responsible for
> + * releasing the lock.
> *

> * Returns the number of pages mapped in success, negative error code
> * for failure.
> @@ -453,11 +453,9 @@ int ib_umem_odp_map_dma_and_lock(struct ib_umem_odp *umem_odp, u64 user_virt,
> break;
> }
> }
> - /* upon success lock should stay on hold for the callee */
> +
> if (!ret)
> ret = dma_index - start_idx;
> - else
> - mutex_unlock(&umem_odp->umem_mutex);
>
> out_put_mm:
> mmput_async(owning_mm);
> diff --git a/drivers/infiniband/hw/mlx5/odp.c b/drivers/infiniband/hw/mlx5/odp.c
> index bc97958818bb..a0de27651586 100644
> --- a/drivers/infiniband/hw/mlx5/odp.c
> +++ b/drivers/infiniband/hw/mlx5/odp.c
> @@ -572,8 +572,10 @@ static int pagefault_real_mr(struct mlx5_ib_mr *mr, struct ib_umem_odp *odp,
> access_mask |= ODP_WRITE_ALLOWED_BIT;
>
> np = ib_umem_odp_map_dma_and_lock(odp, user_va, bcnt, access_mask, fault);
> - if (np < 0)
> + if (np < 0) {
> + mutex_unlock(&odp->umem_mutex);
> return np;
> + }

refer to the comments of ib_umem_odp_map_dma_and_lock:
334 * Returns the number of pages mapped in success, negative error
code
335 * for failure.

I don't think it's correct to release the lock in all failure case, for
example when it reaches below error path.

346 int ib_umem_odp_map_dma_and_lock(struct ib_umem_odp *umem_odp, u64
user_virt,
347 u64 bcnt, u64 access_mask, bool
fault)
348 __acquires(&umem_odp->umem_mutex)

349 {

350 struct task_struct *owning_process = NULL;

351 struct mm_struct *owning_mm = umem_odp->umem.owning_mm;

352 int pfn_index, dma_index, ret = 0, start_idx;

353 unsigned int page_shift, hmm_order, pfn_start_idx;

354 unsigned long num_pfns, current_seq;

355 struct hmm_range range = {};

356 unsigned long timeout;

357

358 if (access_mask == 0)

359 return -EINVAL; <<<<< no lock is hold yet

360

361 if (user_virt < ib_umem_start(umem_odp) ||

362 user_virt + bcnt > ib_umem_end(umem_odp))

363 return -EFAULT; <<<<< no lock is hold yet

Further more, you changed public API's the behavior, do it matter for
other out-of-tree drivers which is using it, i'm not familiar with this,
maybe kernel has no restriction on it ?

>
> /*
> * No need to check whether the MTTs really belong to this MR, since