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

Dan Williams
2021-11-23T03:33:20Z

On Tue, Nov 9, 2021 at 12:33 AM Christoph Hellwig <hch@lst.de> wrote:
>
> 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 <snitzer@redhat.com>
> ---
> 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);

Is it time to add a "DAX" symbol namespace?

>
> -#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) {

Not a problem introduced by this patch, but this needs to be:

if (!IS_ERR_OR_NULL(md->dax_dev)))

...as alloc_dev() calls this after md->dax_dev allocation might have failed.

> + dax_remove_host(md->disk);

> 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;

This leaks the dax_dev. Perhaps this wants devm_alloc_dax() and
devm_dax_add_host() rather than piggybacking on the pmem_release_disk
devm action.

Other changes look good.