dax/bus.c: replace driver-core lock usage by a local rwsem

Patch series "Add DAX ABI for memmap_on_memory", v7.

This series adds sysfs ABI to control memmap_on_memory behavior for DAX
devices.

Patch 1 replaces incorrect device_lock() usage with a local rwsem - this
was identified during review.

Patch 2 is also a preparatory patch that replaces sprintf() for sysfs
operations with sysfs_emit()

Patch 3 adds the missing documentation for the sysfs ABI for DAX regions
and Dax devices.

Patch 4 exports mhp_supports_memmap_on_memory().

Patch 5 adds the new ABI for toggling memmap_on_memory semantics for dax
devices.


This patch (of 5):

The dax driver incorrectly used driver-core device locks to protect
internal dax region and dax device configuration structures.  Replace the
device lock usage with a local rwsem, one each for dax region
configuration and dax device configuration.  As a result of this
conversion, no device_lock() usage remains in dax/bus.c.

Link: https://lkml.kernel.org/r/20240124-vv-dax_abi-v7-0-20d16cb8d23d@intel.com
Link: https://lkml.kernel.org/r/20240124-vv-dax_abi-v7-1-20d16cb8d23d@intel.comSigned-off-by: Vishal Verma <vishal.l.verma@intel.com>
Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Li Zhijian <lizhijian@fujitsu.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/dax/bus.c

@@ -12,6 +12,18 @@
 
 static DEFINE_MUTEX(dax_bus_lock);
 
+/*
+ * All changes to the dax region configuration occur with this lock held
+ * for write.
+ */
+DECLARE_RWSEM(dax_region_rwsem);
+
+/*
+ * All changes to the dax device configuration occur with this lock held
+ * for write.
+ */
+DECLARE_RWSEM(dax_dev_rwsem);
+
 #define DAX_NAME_LEN 30
 struct dax_id {
 	struct list_head list;
@@ -180,7 +192,7 @@ static u64 dev_dax_size(struct dev_dax *dev_dax)
 	u64 size = 0;
 	int i;
 
-	device_lock_assert(&dev_dax->dev);
+	WARN_ON_ONCE(!rwsem_is_locked(&dax_dev_rwsem));
 
 	for (i = 0; i < dev_dax->nr_range; i++)
 		size += range_len(&dev_dax->ranges[i].range);
@@ -194,8 +206,15 @@ static int dax_bus_probe(struct device *dev)
 	struct dev_dax *dev_dax = to_dev_dax(dev);
 	struct dax_region *dax_region = dev_dax->region;
 	int rc;
+	u64 size;
 
-	if (dev_dax_size(dev_dax) == 0 || dev_dax->id < 0)
+	rc = down_read_interruptible(&dax_dev_rwsem);
+	if (rc)
+		return rc;
+	size = dev_dax_size(dev_dax);
+	up_read(&dax_dev_rwsem);
+
+	if (size == 0 || dev_dax->id < 0)
 		return -ENXIO;
 
 	rc = dax_drv->probe(dev_dax);
@@ -283,7 +302,7 @@ static unsigned long long dax_region_avail_size(struct dax_region *dax_region)
 	resource_size_t size = resource_size(&dax_region->res);
 	struct resource *res;
 
-	device_lock_assert(dax_region->dev);
+	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
 
 	for_each_dax_region_resource(dax_region, res)
 		size -= resource_size(res);
@@ -295,10 +314,13 @@ static ssize_t available_size_show(struct device *dev,
 {
 	struct dax_region *dax_region = dev_get_drvdata(dev);
 	unsigned long long size;
+	int rc;
 
-	device_lock(dev);
+	rc = down_read_interruptible(&dax_region_rwsem);
+	if (rc)
+		return rc;
 	size = dax_region_avail_size(dax_region);
-	device_unlock(dev);
+	up_read(&dax_region_rwsem);
 
 	return sprintf(buf, "%llu\n", size);
 }
@@ -314,10 +336,12 @@ static ssize_t seed_show(struct device *dev,
 	if (is_static(dax_region))
 		return -EINVAL;
 
-	device_lock(dev);
+	rc = down_read_interruptible(&dax_region_rwsem);
+	if (rc)
+		return rc;
 	seed = dax_region->seed;
 	rc = sprintf(buf, "%s\n", seed ? dev_name(seed) : "");
-	device_unlock(dev);
+	up_read(&dax_region_rwsem);
 
 	return rc;
 }
@@ -333,14 +357,18 @@ static ssize_t create_show(struct device *dev,
 	if (is_static(dax_region))
 		return -EINVAL;
 
-	device_lock(dev);
+	rc = down_read_interruptible(&dax_region_rwsem);
+	if (rc)
+		return rc;
 	youngest = dax_region->youngest;
 	rc = sprintf(buf, "%s\n", youngest ? dev_name(youngest) : "");
-	device_unlock(dev);
+	up_read(&dax_region_rwsem);
 
 	return rc;
 }
 
+static struct dev_dax *__devm_create_dev_dax(struct dev_dax_data *data);
+
 static ssize_t create_store(struct device *dev, struct device_attribute *attr,
 		const char *buf, size_t len)
 {
@@ -358,7 +386,9 @@ static ssize_t create_store(struct device *dev, struct device_attribute *attr,
 	if (val != 1)
 		return -EINVAL;
 
-	device_lock(dev);
+	rc = down_write_killable(&dax_region_rwsem);
+	if (rc)
+		return rc;
 	avail = dax_region_avail_size(dax_region);
 	if (avail == 0)
 		rc = -ENOSPC;
@@ -369,7 +399,7 @@ static ssize_t create_store(struct device *dev, struct device_attribute *attr,
 			.id = -1,
 			.memmap_on_memory = false,
 		};
-		struct dev_dax *dev_dax = devm_create_dev_dax(&data);
+		struct dev_dax *dev_dax = __devm_create_dev_dax(&data);
 
 		if (IS_ERR(dev_dax))
 			rc = PTR_ERR(dev_dax);
@@ -387,7 +417,7 @@ static ssize_t create_store(struct device *dev, struct device_attribute *attr,
 			rc = len;
 		}
 	}
-	device_unlock(dev);
+	up_write(&dax_region_rwsem);
 
 	return rc;
 }
@@ -417,7 +447,7 @@ static void trim_dev_dax_range(struct dev_dax *dev_dax)
 	struct range *range = &dev_dax->ranges[i].range;
 	struct dax_region *dax_region = dev_dax->region;
 
-	device_lock_assert(dax_region->dev);
+	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
 	dev_dbg(&dev_dax->dev, "delete range[%d]: %#llx:%#llx\n", i,
 		(unsigned long long)range->start,
 		(unsigned long long)range->end);
@@ -435,7 +465,7 @@ static void free_dev_dax_ranges(struct dev_dax *dev_dax)
 		trim_dev_dax_range(dev_dax);
 }
 
-static void unregister_dev_dax(void *dev)
+static void __unregister_dev_dax(void *dev)
 {
 	struct dev_dax *dev_dax = to_dev_dax(dev);
 
@@ -447,6 +477,17 @@ static void unregister_dev_dax(void *dev)
 	put_device(dev);
 }
 
+static void unregister_dev_dax(void *dev)
+{
+	if (rwsem_is_locked(&dax_region_rwsem))
+		return __unregister_dev_dax(dev);
+
+	if (WARN_ON_ONCE(down_write_killable(&dax_region_rwsem) != 0))
+		return;
+	__unregister_dev_dax(dev);
+	up_write(&dax_region_rwsem);
+}
+
 static void dax_region_free(struct kref *kref)
 {
 	struct dax_region *dax_region;
@@ -463,11 +504,10 @@ static void dax_region_put(struct dax_region *dax_region)
 /* a return value >= 0 indicates this invocation invalidated the id */
 static int __free_dev_dax_id(struct dev_dax *dev_dax)
 {
-	struct device *dev = &dev_dax->dev;
 	struct dax_region *dax_region;
 	int rc = dev_dax->id;
 
-	device_lock_assert(dev);
+	WARN_ON_ONCE(!rwsem_is_locked(&dax_dev_rwsem));
 
 	if (!dev_dax->dyn_id || dev_dax->id < 0)
 		return -1;
@@ -480,12 +520,13 @@ static int __free_dev_dax_id(struct dev_dax *dev_dax)
 
 static int free_dev_dax_id(struct dev_dax *dev_dax)
 {
-	struct device *dev = &dev_dax->dev;
 	int rc;
 
-	device_lock(dev);
+	rc = down_write_killable(&dax_dev_rwsem);
+	if (rc)
+		return rc;
 	rc = __free_dev_dax_id(dev_dax);
-	device_unlock(dev);
+	up_write(&dax_dev_rwsem);
 	return rc;
 }
 
@@ -519,8 +560,14 @@ static ssize_t delete_store(struct device *dev, struct device_attribute *attr,
 	if (!victim)
 		return -ENXIO;
 
-	device_lock(dev);
-	device_lock(victim);
+	rc = down_write_killable(&dax_region_rwsem);
+	if (rc)
+		return rc;
+	rc = down_write_killable(&dax_dev_rwsem);
+	if (rc) {
+		up_write(&dax_region_rwsem);
+		return rc;
+	}
 	dev_dax = to_dev_dax(victim);
 	if (victim->driver || dev_dax_size(dev_dax))
 		rc = -EBUSY;
@@ -541,12 +588,12 @@ static ssize_t delete_store(struct device *dev, struct device_attribute *attr,
 		} else
 			rc = -EBUSY;
 	}
-	device_unlock(victim);
+	up_write(&dax_dev_rwsem);
 
 	/* won the race to invalidate the device, clean it up */
 	if (do_del)
 		devm_release_action(dev, unregister_dev_dax, victim);
-	device_unlock(dev);
+	up_write(&dax_region_rwsem);
 	put_device(victim);
 
 	return rc;
@@ -658,16 +705,15 @@ static void dax_mapping_release(struct device *dev)
 	put_device(parent);
 }
 
-static void unregister_dax_mapping(void *data)
+static void __unregister_dax_mapping(void *data)
 {
 	struct device *dev = data;
 	struct dax_mapping *mapping = to_dax_mapping(dev);
 	struct dev_dax *dev_dax = to_dev_dax(dev->parent);
-	struct dax_region *dax_region = dev_dax->region;
 
 	dev_dbg(dev, "%s\n", __func__);
 
-	device_lock_assert(dax_region->dev);
+	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
 
 	dev_dax->ranges[mapping->range_id].mapping = NULL;
 	mapping->range_id = -1;
@@ -675,28 +721,37 @@ static void unregister_dax_mapping(void *data)
 	device_unregister(dev);
 }
 
+static void unregister_dax_mapping(void *data)
+{
+	if (rwsem_is_locked(&dax_region_rwsem))
+		return __unregister_dax_mapping(data);
+
+	if (WARN_ON_ONCE(down_write_killable(&dax_region_rwsem) != 0))
+		return;
+	__unregister_dax_mapping(data);
+	up_write(&dax_region_rwsem);
+}
+
 static struct dev_dax_range *get_dax_range(struct device *dev)
 {
 	struct dax_mapping *mapping = to_dax_mapping(dev);
 	struct dev_dax *dev_dax = to_dev_dax(dev->parent);
-	struct dax_region *dax_region = dev_dax->region;
+	int rc;
 
-	device_lock(dax_region->dev);
+	rc = down_write_killable(&dax_region_rwsem);
+	if (rc)
+		return NULL;
 	if (mapping->range_id < 0) {
-		device_unlock(dax_region->dev);
+		up_write(&dax_region_rwsem);
 		return NULL;
 	}
 
 	return &dev_dax->ranges[mapping->range_id];
 }
 
-static void put_dax_range(struct dev_dax_range *dax_range)
+static void put_dax_range(void)
 {
-	struct dax_mapping *mapping = dax_range->mapping;
-	struct dev_dax *dev_dax = to_dev_dax(mapping->dev.parent);
-	struct dax_region *dax_region = dev_dax->region;
-
-	device_unlock(dax_region->dev);
+	up_write(&dax_region_rwsem);
 }
 
 static ssize_t start_show(struct device *dev,
@@ -709,7 +764,7 @@ static ssize_t start_show(struct device *dev,
 	if (!dax_range)
 		return -ENXIO;
 	rc = sprintf(buf, "%#llx\n", dax_range->range.start);
-	put_dax_range(dax_range);
+	put_dax_range();
 
 	return rc;
 }
@@ -725,7 +780,7 @@ static ssize_t end_show(struct device *dev,
 	if (!dax_range)
 		return -ENXIO;
 	rc = sprintf(buf, "%#llx\n", dax_range->range.end);
-	put_dax_range(dax_range);
+	put_dax_range();
 
 	return rc;
 }
@@ -741,7 +796,7 @@ static ssize_t pgoff_show(struct device *dev,
 	if (!dax_range)
 		return -ENXIO;
 	rc = sprintf(buf, "%#lx\n", dax_range->pgoff);
-	put_dax_range(dax_range);
+	put_dax_range();
 
 	return rc;
 }
@@ -775,7 +830,7 @@ static int devm_register_dax_mapping(struct dev_dax *dev_dax, int range_id)
 	struct device *dev;
 	int rc;
 
-	device_lock_assert(dax_region->dev);
+	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
 
 	if (dev_WARN_ONCE(&dev_dax->dev, !dax_region->dev->driver,
 				"region disabled\n"))
@@ -821,7 +876,7 @@ static int alloc_dev_dax_range(struct dev_dax *dev_dax, u64 start,
 	struct resource *alloc;
 	int i, rc;
 
-	device_lock_assert(dax_region->dev);
+	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
 
 	/* handle the seed alloc special case */
 	if (!size) {
@@ -875,13 +930,12 @@ static int adjust_dev_dax_range(struct dev_dax *dev_dax, struct resource *res, r
 {
 	int last_range = dev_dax->nr_range - 1;
 	struct dev_dax_range *dax_range = &dev_dax->ranges[last_range];
-	struct dax_region *dax_region = dev_dax->region;
 	bool is_shrink = resource_size(res) > size;
 	struct range *range = &dax_range->range;
 	struct device *dev = &dev_dax->dev;
 	int rc;
 
-	device_lock_assert(dax_region->dev);
+	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
 
 	if (dev_WARN_ONCE(dev, !size, "deletion is handled by dev_dax_shrink\n"))
 		return -EINVAL;
@@ -907,10 +961,13 @@ static ssize_t size_show(struct device *dev,
 {
 	struct dev_dax *dev_dax = to_dev_dax(dev);
 	unsigned long long size;
+	int rc;
 
-	device_lock(dev);
+	rc = down_write_killable(&dax_dev_rwsem);
+	if (rc)
+		return rc;
 	size = dev_dax_size(dev_dax);
-	device_unlock(dev);
+	up_write(&dax_dev_rwsem);
 
 	return sprintf(buf, "%llu\n", size);
 }
@@ -1080,17 +1137,27 @@ static ssize_t size_store(struct device *dev, struct device_attribute *attr,
 		return -EINVAL;
 	}
 
-	device_lock(dax_region->dev);
+	rc = down_write_killable(&dax_region_rwsem);
+	if (rc)
+		return rc;
 	if (!dax_region->dev->driver) {
-		device_unlock(dax_region->dev);
-		return -ENXIO;
+		rc = -ENXIO;
+		goto err_region;
 	}
-	device_lock(dev);
+	rc = down_write_killable(&dax_dev_rwsem);
+	if (rc)
+		goto err_dev;
+
 	rc = dev_dax_resize(dax_region, dev_dax, val);
-	device_unlock(dev);
-	device_unlock(dax_region->dev);
 
-	return rc == 0 ? len : rc;
+err_dev:
+	up_write(&dax_dev_rwsem);
+err_region:
+	up_write(&dax_region_rwsem);
+
+	if (rc == 0)
+		return len;
+	return rc;
 }
 static DEVICE_ATTR_RW(size);
 
@@ -1138,18 +1205,24 @@ static ssize_t mapping_store(struct device *dev, struct device_attribute *attr,
 		return rc;
 
 	rc = -ENXIO;
-	device_lock(dax_region->dev);
+	rc = down_write_killable(&dax_region_rwsem);
+	if (rc)
+		return rc;
 	if (!dax_region->dev->driver) {
-		device_unlock(dax_region->dev);
+		up_write(&dax_region_rwsem);
+		return rc;
+	}
+	rc = down_write_killable(&dax_dev_rwsem);
+	if (rc) {
+		up_write(&dax_region_rwsem);
 		return rc;
 	}
-	device_lock(dev);
 
 	to_alloc = range_len(&r);
 	if (alloc_is_aligned(dev_dax, to_alloc))
 		rc = alloc_dev_dax_range(dev_dax, r.start, to_alloc);
-	device_unlock(dev);
-	device_unlock(dax_region->dev);
+	up_write(&dax_dev_rwsem);
+	up_write(&dax_region_rwsem);
 
 	return rc == 0 ? len : rc;
 }
@@ -1196,13 +1269,19 @@ static ssize_t align_store(struct device *dev, struct device_attribute *attr,
 	if (!dax_align_valid(val))
 		return -EINVAL;
 
-	device_lock(dax_region->dev);
+	rc = down_write_killable(&dax_region_rwsem);
+	if (rc)
+		return rc;
 	if (!dax_region->dev->driver) {
-		device_unlock(dax_region->dev);
+		up_write(&dax_region_rwsem);
 		return -ENXIO;
 	}
 
-	device_lock(dev);
+	rc = down_write_killable(&dax_dev_rwsem);
+	if (rc) {
+		up_write(&dax_region_rwsem);
+		return rc;
+	}
 	if (dev->driver) {
 		rc = -EBUSY;
 		goto out_unlock;
@@ -1214,8 +1293,8 @@ static ssize_t align_store(struct device *dev, struct device_attribute *attr,
 	if (rc)
 		dev_dax->align = align_save;
 out_unlock:
-	device_unlock(dev);
-	device_unlock(dax_region->dev);
+	up_write(&dax_dev_rwsem);
+	up_write(&dax_region_rwsem);
 	return rc == 0 ? len : rc;
 }
 static DEVICE_ATTR_RW(align);
@@ -1325,7 +1404,7 @@ static const struct device_type dev_dax_type = {
 	.groups = dax_attribute_groups,
 };
 
-struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
+static struct dev_dax *__devm_create_dev_dax(struct dev_dax_data *data)
 {
 	struct dax_region *dax_region = data->dax_region;
 	struct device *parent = dax_region->dev;
@@ -1440,6 +1519,21 @@ struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
 
 	return ERR_PTR(rc);
 }
+
+struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
+{
+	struct dev_dax *dev_dax;
+	int rc;
+
+	rc = down_write_killable(&dax_region_rwsem);
+	if (rc)
+		return ERR_PTR(rc);
+
+	dev_dax = __devm_create_dev_dax(data);
+	up_write(&dax_region_rwsem);
+
+	return dev_dax;
+}
 EXPORT_SYMBOL_GPL(devm_create_dev_dax);
 
 int __dax_driver_register(struct dax_device_driver *dax_drv,