[PATCH 19/19] block: switch gendisk lookup to a simple xarray

Christoph Hellwig
2020-09-03T08:12:46Z

Now that bdev_map is only used for finding gendisks, we can use
a simple xarray instead of the regions tracking structure for it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
block/genhd.c | 208 ++++++++----------------------------------
include/linux/genhd.h | 7 --
2 files changed, 37 insertions(+), 178 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 3abd764443a6af..6e0789a158f579 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -27,15 +27,7 @@

static struct kobject *block_depr;

-struct bdev_map {
- struct bdev_map *next;
- dev_t dev;
- unsigned long range;
- struct module *owner;
- struct kobject *(*probe)(dev_t, int *, void *);
- int (*lock)(dev_t, void *);
- void *data;
-} *bdev_map[255];
+static DEFINE_XARRAY(bdev_map);
static DEFINE_MUTEX(bdev_map_lock);

/* for extended dynamic devt allocation, currently only one major is used */
@@ -646,85 +638,26 @@ static char *bdevt_str(dev_t devt, char *buf)
return buf;
}

-/*
- * Register device numbers dev..(dev+range-1)
- * range must be nonzero
- * The hash chain is sorted on range, so that subranges can override.
- */
-void blk_register_region(dev_t devt, unsigned long range, struct module *module,
- struct kobject *(*probe)(dev_t, int *, void *),
- int (*lock)(dev_t, void *), void *data)
-{
- unsigned n = MAJOR(devt + range - 1) - MAJOR(devt) + 1;
- unsigned index = MAJOR(devt);
- unsigned i;
- struct bdev_map *p;
-
- n = min(n, 255u);
- p = kmalloc_array(n, sizeof(struct bdev_map), GFP_KERNEL);
- if (p == NULL)
- return;
-
- for (i = 0; i < n; i++, p++) {
- p->owner = module;
- p->probe = probe;
- p->lock = lock;
- p->dev = devt;
- p->range = range;
- p->data = data;
- }
+static void blk_register_region(struct gendisk *disk)
+{
+ int i;

mutex_lock(&bdev_map_lock);
- for (i = 0, p -= n; i < n; i++, p++, index++) {
- struct bdev_map **s = &bdev_map[index % 255];
- while (*s && (*s)->range < range)
- s = &(*s)->next;
- p->next = *s;
- *s = p;
+ for (i = 0; i < disk->minors; i++) {
+ if (xa_insert(&bdev_map, disk_devt(disk) + i, disk, GFP_KERNEL))
+ WARN_ON_ONCE(1);
}
mutex_unlock(&bdev_map_lock);
}
-EXPORT_SYMBOL(blk_register_region);

-void blk_unregister_region(dev_t devt, unsigned long range)
+static void blk_unregister_region(struct gendisk *disk)
{
- unsigned n = MAJOR(devt + range - 1) - MAJOR(devt) + 1;
- unsigned index = MAJOR(devt);
- unsigned i;
- struct bdev_map *found = NULL;
+ int i;

mutex_lock(&bdev_map_lock);
- for (i = 0; i < min(n, 255u); i++, index++) {
- struct bdev_map **s;
- for (s = &bdev_map[index % 255]; *s; s = &(*s)->next) {
- struct bdev_map *p = *s;
- if (p->dev == devt && p->range == range) {
- *s = p->next;
- if (!found)
- found = p;
- break;
- }
- }
- }
+ for (i = 0; i < disk->minors; i++)
+ xa_erase(&bdev_map, disk_devt(disk) + i);
mutex_unlock(&bdev_map_lock);
- kfree(found);
-}
-EXPORT_SYMBOL(blk_unregister_region);
-
-static struct kobject *exact_match(dev_t devt, int *partno, void *data)
-{
- struct gendisk *p = data;
-
- return &disk_to_dev(p)->kobj;
-}
-
-static int exact_lock(dev_t devt, void *data)
-{
- struct gendisk *p = data;
-
- if (!get_disk_and_module(p))
- return -1;
- return 0;
}

static void register_disk(struct device *parent, struct gendisk *disk,
@@ -875,8 +808,7 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
ret = bdi_register(bdi, "%u:%u", MAJOR(devt), MINOR(devt));
WARN_ON(ret);
bdi_set_owner(bdi, dev);
- blk_register_region(disk_devt(disk), disk->minors, NULL,
- exact_match, exact_lock, disk);
+ blk_register_region(disk);
}
register_disk(parent, disk, groups);
if (register_queue)
@@ -989,7 +921,7 @@ void del_gendisk(struct gendisk *disk)
blk_unregister_queue(disk);

if (!(disk->flags & GENHD_FL_HIDDEN))
- blk_unregister_region(disk_devt(disk), disk->minors);
+ blk_unregister_region(disk);
/*
* Remove gendisk pointer from idr so that it cannot be looked up
* while RCU period before freeing gendisk is running to prevent
@@ -1055,54 +987,22 @@ static void request_gendisk_module(dev_t devt)
request_module("block-major-%d", MAJOR(devt));
}

-static struct gendisk *lookup_gendisk(dev_t dev, int *partno)
+static bool get_disk_and_module(struct gendisk *disk)
{
- struct kobject *kobj;
- struct bdev_map *p;
- unsigned long best = ~0UL;
-
-retry:
- mutex_lock(&bdev_map_lock);
- for (p = bdev_map[MAJOR(dev) % 255]; p; p = p->next) {
- struct kobject *(*probe)(dev_t, int *, void *);
- struct module *owner;
- void *data;
-
- if (p->dev > dev || p->dev + p->range - 1 < dev)
- continue;
- if (p->range - 1 >= best)
- break;
- if (!try_module_get(p->owner))
- continue;
- owner = p->owner;
- data = p->data;
- probe = p->probe;
- best = p->range - 1;
- *partno = dev - p->dev;
-
- if (!probe) {
- mutex_unlock(&bdev_map_lock);
- module_put(owner);
- request_gendisk_module(dev);
- goto retry;
- }
+ struct module *owner;

- if (p->lock && p->lock(dev, data) < 0) {
- module_put(owner);
- continue;
- }
- mutex_unlock(&bdev_map_lock);
- kobj = probe(dev, partno, data);
- /* Currently ->owner protects _only_ ->probe() itself. */
+ if (!disk->fops)
+ return false;
+ owner = disk->fops->owner;
+ if (owner && !try_module_get(owner))
+ return false;
+ if (!kobject_get_unless_zero(&disk_to_dev(disk)->kobj)) {
module_put(owner);
- if (kobj)
- return dev_to_disk(kobj_to_dev(kobj));
- goto retry;
+ return false;
}
- mutex_unlock(&bdev_map_lock);
- return NULL;
-}
+ return true;

+}

/**
* get_gendisk - get partitioning information for a given device
@@ -1121,7 +1021,19 @@ struct gendisk *get_gendisk(dev_t devt, int *partno)
might_sleep();

if (MAJOR(devt) != BLOCK_EXT_MAJOR) {
- disk = lookup_gendisk(devt, partno);
+ mutex_lock(&bdev_map_lock);
+ disk = xa_load(&bdev_map, devt);
+ if (!disk) {
+ mutex_unlock(&bdev_map_lock);
+ request_gendisk_module(devt);
+ mutex_lock(&bdev_map_lock);
+ disk = xa_load(&bdev_map, devt);
+ }
+ if (disk && !get_disk_and_module(disk))
+ disk = NULL;
+ if (disk)
+ *partno = devt - disk_devt(disk);
+ mutex_unlock(&bdev_map_lock);
} else {
struct hd_struct *part;

@@ -1325,21 +1237,6 @@ static const struct seq_operations partitions_op = {
};
#endif

-static void bdev_map_init(void)
-{
- struct bdev_map *base;
- int i;
-
- base = kzalloc(sizeof(*base), GFP_KERNEL);
- if (!base)
- panic("cannot allocate bdev_map");
-
- base->dev = 1;
- base->range = ~0 ;
- for (i = 0; i < 255; i++)
- bdev_map[i] = base;
-}
-
static int __init genhd_device_init(void)
{
int error;
@@ -1348,7 +1245,6 @@ static int __init genhd_device_init(void)
error = class_register(&block_class);
if (unlikely(error))
return error;
- bdev_map_init();
blk_dev_init();

register_blkdev(BLOCK_EXT_MAJOR, "blkext");
@@ -1897,35 +1793,6 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
}
EXPORT_SYMBOL(__alloc_disk_node);

-/**
- * get_disk_and_module - increments the gendisk and gendisk fops module refcount
- * @disk: the struct gendisk to increment the refcount for
- *
- * This increments the refcount for the struct gendisk, and the gendisk's
- * fops module owner.
- *
- * Context: Any context.
- */
-struct kobject *get_disk_and_module(struct gendisk *disk)
-{
- struct module *owner;
- struct kobject *kobj;
-
- if (!disk->fops)
- return NULL;
- owner = disk->fops->owner;
- if (owner && !try_module_get(owner))
- return NULL;
- kobj = kobject_get_unless_zero(&disk_to_dev(disk)->kobj);
- if (kobj == NULL) {
- module_put(owner);
- return NULL;
- }
- return kobj;
-
-}
-EXPORT_SYMBOL(get_disk_and_module);
-
/**
* put_disk - decrements the gendisk refcount
* @disk: the struct gendisk to decrement the refcount for
@@ -1962,7 +1829,6 @@ void put_disk_and_module(struct gendisk *disk)
module_put(owner);
}
}
-EXPORT_SYMBOL(put_disk_and_module);

static void set_disk_ro_uevent(struct gendisk *gd, int ro)
{
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index a808afe80a4fec..eac6b31534dea2 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -339,15 +339,8 @@ int blk_add_partitions(struct gendisk *disk, struct block_device *bdev);
int blk_drop_partitions(struct block_device *bdev);

extern struct gendisk *__alloc_disk_node(int minors, int node_id);
-extern struct kobject *get_disk_and_module(struct gendisk *disk);
extern void put_disk(struct gendisk *disk);
extern void put_disk_and_module(struct gendisk *disk);
-extern void blk_register_region(dev_t devt, unsigned long range,
- struct module *module,
- struct kobject *(*probe)(dev_t, int *, void *),
- int (*lock)(dev_t, void *),
- void *data);
-extern void blk_unregister_region(dev_t devt, unsigned long range);

#define alloc_disk_node(minors, node_id) \
({ \
--
2.28.0