Re: [dpdk-dev] [PATCH] mempool: fix mempool virt populate with small chunks

[David Marchand <david.marchand@redhat.com>]

On Thu, Jan 9, 2020 at 2:27 PM Olivier Matz <olivier.matz@6wind.com> wrote:
>
> To populate a mempool with a virtual area, the mempool code calls
> rte_mempool_populate_iova() for each iova-contiguous area. It happens
> (rarely) that this area is too small to store one object. In this case,
> rte_mempool_populate_iova() returns an error, which is forwarded by
> rte_mempool_populate_virt().
>
> This case should not throw an error in
> rte_mempool_populate_virt(). Instead, the area that is too small should
> just be ignored.
>
> To fix this issue, change the return value of
> rte_mempool_populate_iova() to -ENOBUFS when no object can be populated,
> so it can be ignored by the caller. As this would be an API change, add
> a compat wrapper to keep the current API unchanged. The wrapper will be
> removed for 20.11.
>
> Fixes: 354788b60cfd ("mempool: allow populating with unaligned virtual area")
> Cc: stable@dpdk.org
>
> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> ---
>
> Is there a simple way to ensure that we won't forget to remove the
> wrapper for 20.11? Anatoly suggested me to use versioned symbols, but
> it's not clear to me how.
>
>  doc/guides/rel_notes/deprecation.rst |  4 ++++
>  lib/librte_mempool/rte_mempool.c     | 28 +++++++++++++++++++++++-----
>  lib/librte_mempool/rte_mempool.h     |  5 ++++-
>  3 files changed, 31 insertions(+), 6 deletions(-)
>
> diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
> index afa94b43e..b6e89d9a2 100644
> --- a/doc/guides/rel_notes/deprecation.rst
> +++ b/doc/guides/rel_notes/deprecation.rst
> @@ -86,3 +86,7 @@ Deprecation Notices
>    to set new power environment if power environment was already initialized.
>    In this case the function will return -1 unless the environment is unset first
>    (using ``rte_power_unset_env``). Other function usage scenarios will not change.
> +
> +* mempool: starting from v20.11, rte_mempool_populate_iova() will
> +  return -ENOBUFS instead of -EINVAL when there is not enough room to
> +  store one object.
> diff --git a/lib/librte_mempool/rte_mempool.c b/lib/librte_mempool/rte_mempool.c
> index 78d8eb941..bda361ce6 100644
> --- a/lib/librte_mempool/rte_mempool.c
> +++ b/lib/librte_mempool/rte_mempool.c
> @@ -297,8 +297,8 @@ mempool_ops_alloc_once(struct rte_mempool *mp)
>   * zone. Return the number of objects added, or a negative value
>   * on error.
>   */
> -int
> -rte_mempool_populate_iova(struct rte_mempool *mp, char *vaddr,
> +static int
> +__rte_mempool_populate_iova(struct rte_mempool *mp, char *vaddr,
>         rte_iova_t iova, size_t len, rte_mempool_memchunk_free_cb_t *free_cb,
>         void *opaque)
>  {
> @@ -332,7 +332,7 @@ rte_mempool_populate_iova(struct rte_mempool *mp, char *vaddr,
>                 off = RTE_PTR_ALIGN_CEIL(vaddr, RTE_MEMPOOL_ALIGN) - vaddr;
>
>         if (off > len) {
> -               ret = -EINVAL;
> +               ret = -ENOBUFS;
>                 goto fail;
>         }
>
> @@ -343,7 +343,7 @@ rte_mempool_populate_iova(struct rte_mempool *mp, char *vaddr,
>
>         /* not enough room to store one object */
>         if (i == 0) {
> -               ret = -EINVAL;
> +               ret = -ENOBUFS;
>                 goto fail;
>         }
>
> @@ -356,6 +356,22 @@ rte_mempool_populate_iova(struct rte_mempool *mp, char *vaddr,
>         return ret;
>  }
>
> +/* Compat wrapper, to be removed when changing the API is allowed (v20.11). */
> +int
> +rte_mempool_populate_iova(struct rte_mempool *mp, char *vaddr,
> +       rte_iova_t iova, size_t len, rte_mempool_memchunk_free_cb_t *free_cb,
> +       void *opaque)
> +{
> +       int ret;
> +
> +       ret = __rte_mempool_populate_iova(mp, vaddr, iova, len, free_cb,
> +                                       opaque);
> +       if (ret == -ENOBUFS)
> +               ret = -EINVAL;
> +
> +       return ret;
> +}
> +
>  static rte_iova_t
>  get_iova(void *addr)
>  {
> @@ -406,8 +422,10 @@ rte_mempool_populate_virt(struct rte_mempool *mp, char *addr,
>                                 break;
>                 }
>
> -               ret = rte_mempool_populate_iova(mp, addr + off, iova,
> +               ret = __rte_mempool_populate_iova(mp, addr + off, iova,
>                         phys_len, free_cb, opaque);
> +               if (ret == -ENOBUFS)
> +                       continue;
>                 if (ret < 0)
>                         goto fail;
>                 /* no need to call the free callback for next chunks */
> diff --git a/lib/librte_mempool/rte_mempool.h b/lib/librte_mempool/rte_mempool.h
> index f81152af9..c08bb444f 100644
> --- a/lib/librte_mempool/rte_mempool.h
> +++ b/lib/librte_mempool/rte_mempool.h
> @@ -1108,7 +1108,10 @@ rte_mempool_free(struct rte_mempool *mp);
>   * @return
>   *   The number of objects added on success.
>   *   On error, the chunk is not added in the memory list of the
> - *   mempool and a negative errno is returned.
> + *   mempool and a negative errno is returned:
> + *   (-ENOBUFS): not enough room in chunk for one object.
> + *   (-ENOSPC): mempool is already populated.
> + *   (-ENOMEM): allocation failure.

You can't update the doc before this function does return -ENOBUFS.


-- 
David Marchand