[PATCH v3 11/23] device-dax: Kill dax_kmem_res

Dan Williams
2020-08-01T03:42:23Z

Several related issues around this unneeded attribute:

- The dax_kmem_res property allows the kmem driver to stash the adjusted
resource range that was used for the hotplug operation, but that can be
recalculated from the original base range.

- kmem is using an open coded release_resource() + kfree() when an
idiomatic release_mem_region() is sufficient.

- The driver managed resource need only manage the busy flag. Other flags
are of no concern to the kmem driver. In fact if kmem inherits some
memory range that add_memory_driver_managed() rejects that is a
memory-hotplug-core policy that the driver is in no position to
override.

- The implementation trusts that failed remove_memory() results in the
entire resource range remaining pinned busy. The driver need not make
that layering violation assumption and just maintain the busy state in
its local resource.

- The "Hot-remove not yet implemented." comment is stale since hotremove
support is now included.

Cc: David Hildenbrand <david@redhat.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/dax/dax-private.h | 3 -
drivers/dax/kmem.c | 123 +++++++++++++++++++++------------------------
2 files changed, 58 insertions(+), 68 deletions(-)

diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
index 6779f683671d..12a2dbc43b40 100644
--- a/drivers/dax/dax-private.h
+++ b/drivers/dax/dax-private.h
@@ -42,8 +42,6 @@ struct dax_region {
* @dev - device core
* @pgmap - pgmap for memmap setup / lifetime (driver owned)
* @range: resource range for the instance
- * @dax_mem_res: physical address range of hotadded DAX memory
- * @dax_mem_name: name for hotadded DAX memory via add_memory_driver_managed()
*/
struct dev_dax {
struct dax_region *region;
@@ -52,7 +50,6 @@ struct dev_dax {
struct device dev;
struct dev_pagemap *pgmap;
struct range range;
- struct resource *dax_kmem_res;
};

static inline u64 range_len(struct range *range)
diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index 5bb133df147d..77e25361fbeb 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -19,16 +19,24 @@ static const char *kmem_name;
/* Set if any memory will remain added when the driver will be unloaded. */
static bool any_hotremove_failed;

+static struct range dax_kmem_range(struct dev_dax *dev_dax)
+{
+ struct range range;
+
+ /* memory-block align the hotplug range */
+ range.start = ALIGN(dev_dax->range.start, memory_block_size_bytes());
+ range.end = ALIGN_DOWN(dev_dax->range.end + 1,
+ memory_block_size_bytes()) - 1;
+ return range;
+}
+
int dev_dax_kmem_probe(struct device *dev)
{
struct dev_dax *dev_dax = to_dev_dax(dev);
- struct range *range = &dev_dax->range;
- resource_size_t kmem_start;
- resource_size_t kmem_size;
- resource_size_t kmem_end;
- struct resource *new_res;
- const char *new_res_name;
- int numa_node;
+ struct range range = dax_kmem_range(dev_dax);
+ int numa_node = dev_dax->target_node;
+ struct resource *res;
+ char *res_name;
int rc;

/*
@@ -37,109 +45,94 @@ int dev_dax_kmem_probe(struct device *dev)
* could be mixed in a node with faster memory, causing
* unavoidable performance issues.
*/
- numa_node = dev_dax->target_node;
if (numa_node < 0) {
dev_warn(dev, "rejecting DAX region with invalid node: %d\n",
numa_node);
return -EINVAL;
}

- /* Hotplug starting at the beginning of the next block: */
- kmem_start = ALIGN(range->start, memory_block_size_bytes());
-
- kmem_size = range_len(range);
- /* Adjust the size down to compensate for moving up kmem_start: */
- kmem_size -= kmem_start - range->start;
- /* Align the size down to cover only complete blocks: */
- kmem_size &= ~(memory_block_size_bytes() - 1);
- kmem_end = kmem_start + kmem_size;
-
- new_res_name = kstrdup(dev_name(dev), GFP_KERNEL);
- if (!new_res_name)
+ res_name = kstrdup(dev_name(dev), GFP_KERNEL);
+ if (!res_name)
return -ENOMEM;

- /* Region is permanently reserved if hotremove fails. */
- new_res = request_mem_region(kmem_start, kmem_size, new_res_name);
- if (!new_res) {
- dev_warn(dev, "could not reserve region [%pa-%pa]\n",
- &kmem_start, &kmem_end);
- kfree(new_res_name);
+ res = request_mem_region(range.start, range_len(&range), res_name);
+ if (!res) {
+ dev_warn(dev, "could not reserve region [%#llx-%#llx]\n",
+ range.start, range.end);
+ kfree(res_name);
return -EBUSY;
}

/*
- * Set flags appropriate for System RAM. Leave ..._BUSY clear
- * so that add_memory() can add a child resource. Do not
- * inherit flags from the parent since it may set new flags
- * unknown to us that will break add_memory() below.
+ * Temporarily clear busy to allow add_memory_driver_managed()
+ * to claim it.
*/
- new_res->flags = IORESOURCE_SYSTEM_RAM;
+ res->flags &= ~IORESOURCE_BUSY;

/*
* Ensure that future kexec'd kernels will not treat this as RAM
* automatically.
*/
- rc = add_memory_driver_managed(numa_node, new_res->start,
- resource_size(new_res), kmem_name);
+ rc = add_memory_driver_managed(numa_node, res->start,
+ resource_size(res), kmem_name);
+
+ res->flags |= IORESOURCE_BUSY;
if (rc) {
- release_resource(new_res);
- kfree(new_res);
- kfree(new_res_name);
+ release_mem_region(range.start, range_len(&range));
+ kfree(res_name);
return rc;
}
- dev_dax->dax_kmem_res = new_res;
+
+ dev_set_drvdata(dev, res_name);

return 0;
}

#ifdef CONFIG_MEMORY_HOTREMOVE
-static int dev_dax_kmem_remove(struct device *dev)
+static void dax_kmem_release(struct dev_dax *dev_dax)
{
- struct dev_dax *dev_dax = to_dev_dax(dev);
- struct resource *res = dev_dax->dax_kmem_res;
- resource_size_t kmem_start = res->start;
- resource_size_t kmem_size = resource_size(res);
- const char *res_name = res->name;
int rc;
+ struct device *dev = &dev_dax->dev;
+ const char *res_name = dev_get_drvdata(dev);
+ struct range range = dax_kmem_range(dev_dax);

/*
* We have one shot for removing memory, if some memory blocks were not
* offline prior to calling this function remove_memory() will fail, and
* there is no way to hotremove this memory until reboot because device
- * unbind will succeed even if we return failure.
+ * unbind will proceed regardless of the remove_memory result.
*/
- rc = remove_memory(dev_dax->target_node, kmem_start, kmem_size);
- if (rc) {
- any_hotremove_failed = true;
- dev_err(dev,
- "DAX region %pR cannot be hotremoved until the next reboot\n",
- res);
- return rc;
+ rc = remove_memory(dev_dax->target_node, range.start, range_len(&range));
+ if (rc == 0) {
+ release_mem_region(range.start, range_len(&range));
+ dev_set_drvdata(dev, NULL);
+ kfree(res_name);
+ return;
}

- /* Release and free dax resources */
- release_resource(res);
- kfree(res);
- kfree(res_name);
- dev_dax->dax_kmem_res = NULL;
-
- return 0;
+ any_hotremove_failed = true;
+ dev_err(dev, "%#llx-%#llx cannot be hotremoved until the next reboot\n",
+ range.start, range.end);
}
#else
-static int dev_dax_kmem_remove(struct device *dev)
+static void dax_kmem_release(struct dev_dax *dev_dax)
{
/*
- * Without hotremove purposely leak the request_mem_region() for the
- * device-dax range and return '0' to ->remove() attempts. The removal
- * of the device from the driver always succeeds, but the region is
- * permanently pinned as reserved by the unreleased
- * request_mem_region().
+ * Without hotremove purposely leak the request_mem_region() for
+ * the device-dax range attempts. The removal of the device from
+ * the driver always succeeds, but the region is permanently
+ * pinned as reserved by the unreleased request_mem_region().
*/
any_hotremove_failed = true;
- return 0;
}
#endif /* CONFIG_MEMORY_HOTREMOVE */

+static int dev_dax_kmem_remove(struct device *dev)
+{
+ dax_kmem_release(to_dev_dax(dev));
+ return 0;
+}
+
static struct dax_device_driver device_dax_kmem_driver = {
.drv = {
.probe = dev_dax_kmem_probe,