Hi Aneesh, Thanks for looking into this patch.
"Aneesh Kumar K.V" aneesh.kumar@linux.ibm.com writes:
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,
For a synchronous dax region, writes arent expected to require any flushing (or deep-flush) so this function should ideally return '0' in such a case. Hence I had added the test for ND_REGION_ASYNC region flag.
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}
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