dax: Introduce alloc_dev_dax_id()

The reference counting of dax_region objects is needlessly complicated,
has lead to confusion [1], and has hidden a bug [2]. Towards cleaning up
that mess introduce alloc_dev_dax_id() to minimize the holding of a
dax_region reference to only what dev_dax_release() needs, the
dax_region->ida.

Part of the reason for the mess was the design to dereference a
dax_region in all cases in free_dev_dax_id() even if the id was
statically assigned by the upper level dax_region driver. Remove the
need to call "is_static(dax_region)" by tracking whether the id is
dynamic directly in the dev_dax instance itself.

With that flag the dax_region pinning and release per dev_dax instance
can move to alloc_dev_dax_id() and free_dev_dax_id() respectively.

A follow-on cleanup address the unnecessary references in the dax_region
setup and drivers.

Fixes: 0f3da14a4f05 ("device-dax: introduce 'seed' devices")
Link: http://lore.kernel.org/r/20221203095858.612027-1-liuyongqiang13@huawei.com
Link: http://lore.kernel.org/r/3cf0890b-4eb0-e70e-cd9c-2ecc3d496263@hpe.com
Reported-by: Yongqiang Liu <liuyongqiang13@huawei.com>
Reported-by: Paul Cassella <cassella@hpe.com>
Reported-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/168577284563.1672036.13493034988900989554.stgit@dwillia2-xfh.jf.intel.com
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index c99ea08aafc322fec97bb418c396eef87d6e0ed4..a4cc3eca774f059e9e824bd648d1b673d40775c0 100644 (file)
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -446,18 +446,34 @@ static void unregister_dev_dax(void *dev)
        put_device(dev);
 }
 
+static void dax_region_free(struct kref *kref)
+{
+       struct dax_region *dax_region;
+
+       dax_region = container_of(kref, struct dax_region, kref);
+       kfree(dax_region);
+}
+
+void dax_region_put(struct dax_region *dax_region)
+{
+       kref_put(&dax_region->kref, dax_region_free);
+}
+EXPORT_SYMBOL_GPL(dax_region_put);
+
 /* a return value >= 0 indicates this invocation invalidated the id */
 static int __free_dev_dax_id(struct dev_dax *dev_dax)
 {
-       struct dax_region *dax_region = dev_dax->region;
        struct device *dev = &dev_dax->dev;
+       struct dax_region *dax_region;
        int rc = dev_dax->id;
 
        device_lock_assert(dev);
 
-       if (is_static(dax_region) || dev_dax->id < 0)
+       if (!dev_dax->dyn_id || dev_dax->id < 0)
                return -1;
+       dax_region = dev_dax->region;
        ida_free(&dax_region->ida, dev_dax->id);
+       dax_region_put(dax_region);
        dev_dax->id = -1;
        return rc;
 }
@@ -473,6 +489,20 @@ static int free_dev_dax_id(struct dev_dax *dev_dax)
        return rc;
 }
 
+static int alloc_dev_dax_id(struct dev_dax *dev_dax)
+{
+       struct dax_region *dax_region = dev_dax->region;
+       int id;
+
+       id = ida_alloc(&dax_region->ida, GFP_KERNEL);
+       if (id < 0)
+               return id;
+       kref_get(&dax_region->kref);
+       dev_dax->dyn_id = true;
+       dev_dax->id = id;
+       return id;
+}
+
 static ssize_t delete_store(struct device *dev, struct device_attribute *attr,
                const char *buf, size_t len)
 {
@@ -560,20 +590,6 @@ static const struct attribute_group *dax_region_attribute_groups[] = {
        NULL,
 };
 
-static void dax_region_free(struct kref *kref)
-{
-       struct dax_region *dax_region;
-
-       dax_region = container_of(kref, struct dax_region, kref);
-       kfree(dax_region);
-}
-
-void dax_region_put(struct dax_region *dax_region)
-{
-       kref_put(&dax_region->kref, dax_region_free);
-}
-EXPORT_SYMBOL_GPL(dax_region_put);
-
 static void dax_region_unregister(void *region)
 {
        struct dax_region *dax_region = region;
@@ -1297,12 +1313,10 @@ static const struct attribute_group *dax_attribute_groups[] = {
 static void dev_dax_release(struct device *dev)
 {
        struct dev_dax *dev_dax = to_dev_dax(dev);
-       struct dax_region *dax_region = dev_dax->region;
        struct dax_device *dax_dev = dev_dax->dax_dev;
 
        put_dax(dax_dev);
        free_dev_dax_id(dev_dax);
-       dax_region_put(dax_region);
        kfree(dev_dax->pgmap);
        kfree(dev_dax);
 }
@@ -1326,6 +1340,7 @@ struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
        if (!dev_dax)
                return ERR_PTR(-ENOMEM);
 
+       dev_dax->region = dax_region;
        if (is_static(dax_region)) {
                if (dev_WARN_ONCE(parent, data->id < 0,
                                "dynamic id specified to static region\n")) {
@@ -1341,13 +1356,11 @@ struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
                        goto err_id;
                }
 
-               rc = ida_alloc(&dax_region->ida, GFP_KERNEL);
+               rc = alloc_dev_dax_id(dev_dax);
                if (rc < 0)
                        goto err_id;
-               dev_dax->id = rc;
        }
 
-       dev_dax->region = dax_region;
        dev = &dev_dax->dev;
        device_initialize(dev);
        dev_set_name(dev, "dax%d.%d", dax_region->id, dev_dax->id);
@@ -1388,7 +1401,6 @@ struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
        dev_dax->target_node = dax_region->target_node;
        dev_dax->align = dax_region->align;
        ida_init(&dev_dax->ida);
-       kref_get(&dax_region->kref);
 
        inode = dax_inode(dax_dev);
        dev->devt = inode->i_rdev;

diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
index db032680d941bfffc5fcbaa922ff4a24d510048e..27cf2daaaa795ad9b8236b985d01aa0e6cea5c40 100644 (file)
--- a/drivers/dax/dax-private.h
+++ b/drivers/dax/dax-private.h
@@ -52,7 +52,8 @@ struct dax_mapping {
  * @region - parent region
  * @dax_dev - core dax functionality
  * @target_node: effective numa node if dev_dax memory range is onlined
- * @id: ida allocated id
+ * @dyn_id: is this a dynamic or statically created instance
+ * @id: ida allocated id when the dax_region is not static
  * @ida: mapping id allocator
  * @dev - device core
  * @pgmap - pgmap for memmap setup / lifetime (driver owned)
@@ -64,6 +65,7 @@ struct dev_dax {
        struct dax_device *dax_dev;
        unsigned int align;
        int target_node;
+       bool dyn_id;
        int id;
        struct ida ida;
        struct device dev;