Hi Vaibhav,
In case a platform doesn't provide explicit flush-hints but provides an explicit flush callback, 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'.
In case of async flush callback, do we still need "deep_flush" ?
Thanks, Pankaj
Fix this by updating nvdimm_has_flush() adding a condition to nvdimm_has_flush() to test if a 'region->flush' callback is assigned. Also remove explicit test for 'nd_region->ndr_mapping' since regions may need 'flush' without any explicit mappings as in case of virtio-pmem.
References: [1] "powerpc/papr_scm: Implement support for H_SCM_FLUSH hcall" https://lore.kernel.org/linux-nvdimm/161703936121.36.7260632399582101498.stg...
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:
v3:
- Removed the test for ND_REGION_SYNC to handle case where a synchronous region still wants to expose a deep-flush function. [ Aneesh ]
- Updated patch title and description from previous patch https://lore.kernel.org/linux-nvdimm/5e64778d-bf48-9f10-7d3d-5e530e5db590@li...
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..c4b17bdd527f 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 (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;}
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