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

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

On Mon, Apr 5, 2021 at 4:31 AM Aneesh Kumar K.V
<aneesh.kumar@linux.ibm.com> wrote:
>
> Vaibhav Jain <vaibhav@linux.ibm.com> writes:
>
> > 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.
> >
>
> May be this should have
> Fixes: c5d4355d10d4 ("libnvdimm: nd_region flush callback support")

Yes, thanks for that.

>
> Without this we will mark the pmem disk not having FUA support?

Yes.

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