From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Vaibhav Jain <vaibhav@linux.ibm.com>, linux-nvdimm@lists.01.org
Cc: Vaibhav Jain <vaibhav@linux.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Shivaprasad G Bhat <sbhat@linux.ibm.com>,
stable@vger.kernel.org
Subject: Re: [PATCH v2] libnvdimm/region: Update nvdimm_has_flush() to handle ND_REGION_ASYNC
Date: Tue, 06 Apr 2021 10:43:00 +0530 [thread overview]
Message-ID: <874kgk6lnn.fsf@linux.ibm.com> (raw)
In-Reply-To: <20210406032233.490596-1-vaibhav@linux.ibm.com>
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.
>
> Similar problem is also seen with virtio-pmem where the 'deep_flush'
> sysfs attribute is not visible as in absence of any registered nvdimm,
> 'nd_region->ndr_mappings == 0'.
>
> Fix this by updating nvdimm_has_flush() adding a condition to
> nvdimm_has_flush() testing for ND_REGION_ASYNC flag on the region
> and see if a 'region->flush' callback is assigned. Also remove
> explicit test for 'nd_region->ndr_mapping' since regions can be marked
> 'ND_REGION_SYNC' without any explicit mappings as in case of
> virtio-pmem.
Do we need to check for ND_REGION_ASYNC? What if the backend wants to
provide a synchronous dax region but with different deep flush semantic
than writing to wpq flush address?
ie,
>
> References:
> [1] "powerpc/papr_scm: Implement support for H_SCM_FLUSH hcall"
> https://lore.kernel.org/linux-nvdimm/161703936121.36.7260632399 582101498.stgit@e1fbed493c87
>
> Cc: <stable@vger.kernel.org>
> Fixes: c5d4355d10d4 ("libnvdimm: nd_region flush callback support")
> Reported-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
> ---
> Changelog:
>
> v2:
> * Added the fixes tag and addressed the patch to stable tree [ Aneesh ]
> * Updated patch description to address the virtio-pmem case.
> * Removed test for 'nd_region->ndr_mappings' from beginning of
> nvdimm_has_flush() to handle the virtio-pmem case.
> ---
> drivers/nvdimm/region_devs.c | 14 +++++++++-----
> 1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
> index ef23119db574..cdf5eb6fa425 100644
> --- a/drivers/nvdimm/region_devs.c
> +++ b/drivers/nvdimm/region_devs.c
> @@ -1234,11 +1234,15 @@ int nvdimm_has_flush(struct nd_region *nd_region)
> {
> int i;
>
> - /* no nvdimm or pmem api == flushing capability unknown */
> - if (nd_region->ndr_mappings == 0
> - || !IS_ENABLED(CONFIG_ARCH_HAS_PMEM_API))
> + /* no pmem api == flushing capability unknown */
> + if (!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;
> +
if (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 +1253,8 @@ 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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next prev parent reply other threads:[~2021-04-06 5:13 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-06 3:22 [PATCH v2] libnvdimm/region: Update nvdimm_has_flush() to handle ND_REGION_ASYNC Vaibhav Jain
2021-04-06 5:13 ` Aneesh Kumar K.V [this message]
2021-04-06 11:37 ` Vaibhav Jain
2021-04-06 12:05 ` Aneesh Kumar K.V
2021-04-08 10:48 ` Vaibhav Jain
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