Re: [PATCH] libnvdimm/region: Update nvdimm_has_flush() to handle ND_REGION_ASYNC

[Dan Williams <dan.j.williams@intel.com>]

On Fri, Apr 2, 2021 at 2:26 AM Vaibhav Jain <vaibhav@linux.ibm.com> wrote:
>
> In case a platform doesn't provide explicit flush-hints but provides an
> explicit flush callback via ND_REGION_ASYNC region flag, then
> nvdimm_has_flush() still returns '0' indicating that writes do not
> require flushing. This happens on PPC64 with patch at [1] applied,
> where 'deep_flush' of a region was denied even though an explicit
> flush function was provided.
>
> Fix this by adding a condition to nvdimm_has_flush() to test for the
> ND_REGION_ASYNC flag on the region and see if a 'region->flush'
> callback is assigned.

Looks good.

>
> References:
> [1] "powerpc/papr_scm: Implement support for H_SCM_FLUSH hcall"
> https://lore.kernel.org/linux-nvdimm/161703936121.36.7260632399 582101498.stgit@e1fbed493c87

Looks like a typo happened in that link, I can fix that up. I'll also
change this to the canonical "Link:" tag for references.

>
> Reported-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
> ---
>  drivers/nvdimm/region_devs.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
> index ef23119db574..e05cc9f8a9fd 100644
> --- a/drivers/nvdimm/region_devs.c
> +++ b/drivers/nvdimm/region_devs.c
> @@ -1239,6 +1239,11 @@ int nvdimm_has_flush(struct nd_region *nd_region)
>                         || !IS_ENABLED(CONFIG_ARCH_HAS_PMEM_API))
>                 return -ENXIO;
>
> +       /* Test if an explicit flush function is defined */
> +       if (test_bit(ND_REGION_ASYNC, &nd_region->flags) && nd_region->flush)
> +               return 1;
> +
> +       /* Test if any flush hints for the region are available */
>         for (i = 0; i < nd_region->ndr_mappings; i++) {
>                 struct nd_mapping *nd_mapping = &nd_region->mapping[i];
>                 struct nvdimm *nvdimm = nd_mapping->nvdimm;
> @@ -1249,8 +1254,8 @@ int nvdimm_has_flush(struct nd_region *nd_region)
>         }
>
>         /*
> -        * The platform defines dimm devices without hints, assume
> -        * platform persistence mechanism like ADR
> +        * The platform defines dimm devices without hints nor explicit flush,
> +        * assume platform persistence mechanism like ADR
>          */
>         return 0;
>  }
> --
> 2.30.2
>
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