linux-kernel - [PATCH RFC 4/4] dax/bus: Remove unnecessary reference in alloc_dax

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Message-Id: <20230602-dax-region-put-v1-4-d8668f335d45@intel.com>
Date:   Fri, 02 Jun 2023 19:09:24 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joao Martins <joao.m.martins@...cle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     Yongqiang Liu <liuyongqiang13@...wei.com>,
        Paul Cassella <cassella@....com>, linux-kernel@...r.kernel.org,
        nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org,
        Ira Weiny <ira.weiny@...el.com>
Subject: [PATCH RFC 4/4] dax/bus: Remove unnecessary reference in
 alloc_dax_region()

All the callers to alloc_dax_region() maintain the device associated
with the dax_region until the dax_region is referenced by the dax_dev
they are creating.

Remove the extra kref that alloc_dax_region() takes.  Add a comment to
clarify the reference counting should additional callers be grown later.

Cc: Yongqiang Liu <liuyongqiang13@...wei.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Paul Cassella <cassella@....com>
Signed-off-by: Ira Weiny <ira.weiny@...el.com>
---
 drivers/dax/bus.c       | 13 ++++++-------
 drivers/dax/cxl.c       |  4 ----
 drivers/dax/hmem/hmem.c |  3 ---
 drivers/dax/pmem.c      |  8 +-------
 4 files changed, 7 insertions(+), 21 deletions(-)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 899e29d107b4..ed34d8aa6b26 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -583,7 +583,11 @@ static void dax_region_unregister(void *region)
 	dax_region_put(dax_region);
 }
 
-/* The dax_region reference returned should be dropped with dax_region_put() */
+/*
+ * Caller is responsible to ensure the parent device stays live while the
+ * returned dax_region is in use.  Or as is typically the case, a separate
+ * reference should be taken.
+ */
 struct dax_region *alloc_dax_region(struct device *parent, int region_id,
 		struct range *range, int target_node, unsigned int align,
 		unsigned long flags)
@@ -626,13 +630,8 @@ struct dax_region *alloc_dax_region(struct device *parent, int region_id,
 		return NULL;
 	}
 
-	/* Hold a reference to return to the caller */
-	kref_get(&dax_region->kref);
-	if (devm_add_action_or_reset(parent, dax_region_unregister,
-				     dax_region)) {
-		kref_put(&dax_region->kref, dax_region_free);
+	if (devm_add_action_or_reset(parent, dax_region_unregister, dax_region))
 		return NULL;
-	}
 	return dax_region;
 }
 EXPORT_SYMBOL_GPL(alloc_dax_region);
diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c
index bbfe71cf4325..5ad600ee68b3 100644
--- a/drivers/dax/cxl.c
+++ b/drivers/dax/cxl.c
@@ -29,10 +29,6 @@ static int cxl_dax_region_probe(struct device *dev)
 		.size = range_len(&cxlr_dax->hpa_range),
 	};
 	dev_dax = devm_create_dev_dax(&data);
-
-	/* child dev_dax instances now own the lifetime of the dax_region */
-	dax_region_put(dax_region);
-
 	return IS_ERR(dev_dax) ? PTR_ERR(dev_dax) : 0;
 }
 
diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
index b4831a3d3934..46e1b343f26e 100644
--- a/drivers/dax/hmem/hmem.c
+++ b/drivers/dax/hmem/hmem.c
@@ -39,9 +39,6 @@ static int dax_hmem_probe(struct platform_device *pdev)
 		.size = region_idle ? 0 : range_len(&mri->range),
 	};
 	dev_dax = devm_create_dev_dax(&data);
-
-	/* child dev_dax instances now own the lifetime of the dax_region */
-	dax_region_put(dax_region);
 	return IS_ERR(dev_dax) ? PTR_ERR(dev_dax) : 0;
 }
 
diff --git a/drivers/dax/pmem.c b/drivers/dax/pmem.c
index f050ea78bb83..a4f016d7f4f5 100644
--- a/drivers/dax/pmem.c
+++ b/drivers/dax/pmem.c
@@ -13,7 +13,6 @@ static struct dev_dax *__dax_pmem_probe(struct device *dev)
 	int rc, id, region_id;
 	resource_size_t offset;
 	struct nd_pfn_sb *pfn_sb;
-	struct dev_dax *dev_dax;
 	struct dev_dax_data data;
 	struct nd_namespace_io *nsio;
 	struct dax_region *dax_region;
@@ -65,12 +64,7 @@ static struct dev_dax *__dax_pmem_probe(struct device *dev)
 		.pgmap = &pgmap,
 		.size = range_len(&range),
 	};
-	dev_dax = devm_create_dev_dax(&data);
-
-	/* child dev_dax instances now own the lifetime of the dax_region */
-	dax_region_put(dax_region);
-
-	return dev_dax;
+	return devm_create_dev_dax(&data);
 }
 
 static int dax_pmem_probe(struct device *dev)

-- 
2.40.0