Re: [PATCH 04/29] dax: simplify the dax_device <-> gendisk association

Replace the dax_host_hash with an xarray indexed by the pointer value
of the gendisk, and require explicitly calls from the block drivers that
want to associate their gendisk with a dax_device.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Mike Snitzer <redacted>
---
 drivers/dax/bus.c            |   6 +-
 drivers/dax/super.c          | 106 +++++++++--------------------------
 drivers/md/dm.c              |   6 +-
 drivers/nvdimm/pmem.c        |   8 ++-
 drivers/s390/block/dcssblk.c |  11 +++-
 fs/fuse/virtio_fs.c          |   2 +-
 include/linux/dax.h          |  19 +++++--
 7 files changed, 62 insertions(+), 96 deletions(-)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 6cc4da4c713d9..bd7af2f7c5b0a 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c

@@ -1323,10 +1323,10 @@ struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
        }

        /*
-        * No 'host' or dax_operations since there is no access to this
-        * device outside of mmap of the resulting character device.
+        * No dax_operations since there is no access to this device outside of
+        * mmap of the resulting character device.
         */
-       dax_dev = alloc_dax(dev_dax, NULL, NULL, DAXDEV_F_SYNC);
+       dax_dev = alloc_dax(dev_dax, NULL, DAXDEV_F_SYNC);
        if (IS_ERR(dax_dev)) {
                rc = PTR_ERR(dax_dev);
                goto err_alloc_dax;

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index e20d0cef10a18..9383c11b21853 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c

@@ -7,10 +7,8 @@
 #include <linux/mount.h>
 #include <linux/pseudo_fs.h>
 #include <linux/magic.h>
-#include <linux/genhd.h>
 #include <linux/pfn_t.h>
 #include <linux/cdev.h>
-#include <linux/hash.h>
 #include <linux/slab.h>
 #include <linux/uio.h>
 #include <linux/dax.h>

@@ -26,10 +24,8 @@
  * @flags: state and boolean properties
  */
 struct dax_device {
-       struct hlist_node list;
        struct inode inode;
        struct cdev cdev;
-       const char *host;
        void *private;
        unsigned long flags;
        const struct dax_operations *ops;

@@ -42,10 +38,6 @@ static DEFINE_IDA(dax_minor_ida);
 static struct kmem_cache *dax_cache __read_mostly;
 static struct super_block *dax_superblock __read_mostly;

-#define DAX_HASH_SIZE (PAGE_SIZE / sizeof(struct hlist_head))
-static struct hlist_head dax_host_list[DAX_HASH_SIZE];
-static DEFINE_SPINLOCK(dax_host_lock);
-
 int dax_read_lock(void)
 {
        return srcu_read_lock(&dax_srcu);

@@ -58,13 +50,22 @@ void dax_read_unlock(int id)
 }
 EXPORT_SYMBOL_GPL(dax_read_unlock);

-static int dax_host_hash(const char *host)
+#if defined(CONFIG_BLOCK) && defined(CONFIG_FS_DAX)
+#include <linux/blkdev.h>
+
+static DEFINE_XARRAY(dax_hosts);
+
+int dax_add_host(struct dax_device *dax_dev, struct gendisk *disk)
 {
-       return hashlen_hash(hashlen_string("DAX", host)) % DAX_HASH_SIZE;
+       return xa_insert(&dax_hosts, (unsigned long)disk, dax_dev, GFP_KERNEL);
 }
+EXPORT_SYMBOL_GPL(dax_add_host);

-#if defined(CONFIG_BLOCK) && defined(CONFIG_FS_DAX)
-#include <linux/blkdev.h>
+void dax_remove_host(struct gendisk *disk)
+{
+       xa_erase(&dax_hosts, (unsigned long)disk);
+}
+EXPORT_SYMBOL_GPL(dax_remove_host);

 int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
                pgoff_t *pgoff)

@@ -82,40 +83,23 @@ EXPORT_SYMBOL(bdev_dax_pgoff);

 /**
  * dax_get_by_host() - temporary lookup mechanism for filesystem-dax
- * @host: alternate name for the device registered by a dax driver
+ * @bdev: block device to find a dax_device for
  */
-static struct dax_device *dax_get_by_host(const char *host)
+struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
 {
-       struct dax_device *dax_dev, *found = NULL;
-       int hash, id;
+       struct dax_device *dax_dev;
+       int id;

-       if (!host)
+       if (!blk_queue_dax(bdev->bd_disk->queue))
                return NULL;

-       hash = dax_host_hash(host);
-
        id = dax_read_lock();
-       spin_lock(&dax_host_lock);
-       hlist_for_each_entry(dax_dev, &dax_host_list[hash], list) {
-               if (!dax_alive(dax_dev)
-                               || strcmp(host, dax_dev->host) != 0)
-                       continue;
-
-               if (igrab(&dax_dev->inode))
-                       found = dax_dev;
-               break;
-       }
-       spin_unlock(&dax_host_lock);
+       dax_dev = xa_load(&dax_hosts, (unsigned long)bdev->bd_disk);
+       if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode))
+               dax_dev = NULL;
        dax_read_unlock(id);

-       return found;
-}
-
-struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
-{
-       if (!blk_queue_dax(bdev->bd_disk->queue))
-               return NULL;
-       return dax_get_by_host(bdev->bd_disk->disk_name);
+       return dax_dev;
 }
 EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);

@@ -361,12 +345,7 @@ void kill_dax(struct dax_device *dax_dev)
                return;

        clear_bit(DAXDEV_ALIVE, &dax_dev->flags);
-
        synchronize_srcu(&dax_srcu);
-
-       spin_lock(&dax_host_lock);
-       hlist_del_init(&dax_dev->list);
-       spin_unlock(&dax_host_lock);
 }
 EXPORT_SYMBOL_GPL(kill_dax);

@@ -398,8 +377,6 @@ static struct dax_device *to_dax_dev(struct inode *inode)
 static void dax_free_inode(struct inode *inode)
 {
        struct dax_device *dax_dev = to_dax_dev(inode);
-       kfree(dax_dev->host);
-       dax_dev->host = NULL;
        if (inode->i_rdev)
                ida_simple_remove(&dax_minor_ida, iminor(inode));
        kmem_cache_free(dax_cache, dax_dev);

@@ -474,54 +451,25 @@ static struct dax_device *dax_dev_get(dev_t devt)
        return dax_dev;
 }

-static void dax_add_host(struct dax_device *dax_dev, const char *host)
-{
-       int hash;
-
-       /*
-        * Unconditionally init dax_dev since it's coming from a
-        * non-zeroed slab cache
-        */
-       INIT_HLIST_NODE(&dax_dev->list);
-       dax_dev->host = host;
-       if (!host)
-               return;
-
-       hash = dax_host_hash(host);
-       spin_lock(&dax_host_lock);
-       hlist_add_head(&dax_dev->list, &dax_host_list[hash]);
-       spin_unlock(&dax_host_lock);
-}
-
-struct dax_device *alloc_dax(void *private, const char *__host,
-               const struct dax_operations *ops, unsigned long flags)
+struct dax_device *alloc_dax(void *private, const struct dax_operations *ops,
+               unsigned long flags)
 {
        struct dax_device *dax_dev;
-       const char *host;
        dev_t devt;
        int minor;

-       if (ops && !ops->zero_page_range) {
-               pr_debug("%s: error: device does not provide dax"
-                        " operation zero_page_range()\n",
-                        __host ? __host : "Unknown");
+       if (WARN_ON_ONCE(ops && !ops->zero_page_range))
                return ERR_PTR(-EINVAL);
-       }
-
-       host = kstrdup(__host, GFP_KERNEL);
-       if (__host && !host)
-               return ERR_PTR(-ENOMEM);

        minor = ida_simple_get(&dax_minor_ida, 0, MINORMASK+1, GFP_KERNEL);
        if (minor < 0)
-               goto err_minor;
+               return ERR_PTR(-ENOMEM);

        devt = MKDEV(MAJOR(dax_devt), minor);
        dax_dev = dax_dev_get(devt);
        if (!dax_dev)
                goto err_dev;

-       dax_add_host(dax_dev, host);
        dax_dev->ops = ops;
        dax_dev->private = private;
        if (flags & DAXDEV_F_SYNC)

@@ -531,8 +479,6 @@ struct dax_device *alloc_dax(void *private, const char *__host,

  err_dev:
        ida_simple_remove(&dax_minor_ida, minor);
- err_minor:
-       kfree(host);
        return ERR_PTR(-ENOMEM);
 }
 EXPORT_SYMBOL_GPL(alloc_dax);

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 893fca738a3d8..782a076f61f81 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c

@@ -1683,6 +1683,7 @@ static void cleanup_mapped_device(struct mapped_device *md)
        bioset_exit(&md->io_bs);

        if (md->dax_dev) {

                kill_dax(md->dax_dev);
                put_dax(md->dax_dev);
                md->dax_dev = NULL;

@@ -1784,10 +1785,11 @@ static struct mapped_device *alloc_dev(int minor)
        sprintf(md->disk->disk_name, "dm-%d", minor);

        if (IS_ENABLED(CONFIG_FS_DAX)) {
-               md->dax_dev = alloc_dax(md, md->disk->disk_name,
-                                       &dm_dax_ops, 0);
+               md->dax_dev = alloc_dax(md, &dm_dax_ops, 0);
                if (IS_ERR(md->dax_dev))
                        goto bad;
+               if (dax_add_host(md->dax_dev, md->disk))
+                       goto bad;
        }

        format_dev_t(md->name, MKDEV(_major, minor));

diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 9cc0d0ebfad16..8783ad7370856 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c

@@ -379,6 +379,7 @@ static void pmem_release_disk(void *__pmem)
 {
        struct pmem_device *pmem = __pmem;

+       dax_remove_host(pmem->disk);
        kill_dax(pmem->dax_dev);
        put_dax(pmem->dax_dev);
        del_gendisk(pmem->disk);

@@ -495,10 +496,11 @@ static int pmem_attach_disk(struct device *dev,

        if (is_nvdimm_sync(nd_region))
                flags = DAXDEV_F_SYNC;
-       dax_dev = alloc_dax(pmem, disk->disk_name, &pmem_dax_ops, flags);
-       if (IS_ERR(dax_dev)) {
+       dax_dev = alloc_dax(pmem, &pmem_dax_ops, flags);
+       if (IS_ERR(dax_dev))
                return PTR_ERR(dax_dev);
-       }
+       if (dax_add_host(dax_dev, disk))
+               return -ENOMEM;