None of the complicated overlapping regions bits of the kobj_map are
required for the character device lookup, so just a trivial xarray
instead.

Signed-off-by: Christoph Hellwig <h...@lst.de>
Reviewed-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 fs/char_dev.c | 94 +++++++++++++++++++++++++--------------------------
 fs/dcache.c   |  1 -
 fs/internal.h |  5 ---
 3 files changed, 47 insertions(+), 53 deletions(-)

diff --git a/fs/char_dev.c b/fs/char_dev.c
index ba0ded7842a779..f9a983d2d1a975 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -17,7 +17,6 @@
 #include <linux/seq_file.h>
 
 #include <linux/kobject.h>
-#include <linux/kobj_map.h>
 #include <linux/cdev.h>
 #include <linux/mutex.h>
 #include <linux/backing-dev.h>
@@ -25,8 +24,7 @@
 
 #include "internal.h"
 
-static struct kobj_map *cdev_map;
-
+static DEFINE_XARRAY(cdev_map);
 static DEFINE_MUTEX(chrdevs_lock);
 
 #define CHRDEV_MAJOR_HASH_SIZE 255
@@ -367,6 +365,29 @@ void cdev_put(struct cdev *p)
        }
 }
 
+static struct cdev *cdev_lookup(dev_t dev)
+{
+       struct cdev *cdev;
+
+retry:
+       mutex_lock(&chrdevs_lock);
+       cdev = xa_load(&cdev_map, dev);
+       if (!cdev) {
+               mutex_unlock(&chrdevs_lock);
+
+               if (request_module("char-major-%d-%d",
+                                  MAJOR(dev), MINOR(dev)) > 0)
+                       /* Make old-style 2.4 aliases work */
+                       request_module("char-major-%d", MAJOR(dev));
+               goto retry;
+       }
+
+       if (!cdev_get(cdev))
+               cdev = NULL;
+       mutex_unlock(&chrdevs_lock);
+       return cdev;
+}
+
 /*
  * Called every time a character special file is opened
  */
@@ -380,13 +401,10 @@ static int chrdev_open(struct inode *inode, struct file 
*filp)
        spin_lock(&cdev_lock);
        p = inode->i_cdev;
        if (!p) {
-               struct kobject *kobj;
-               int idx;
                spin_unlock(&cdev_lock);
-               kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
-               if (!kobj)
+               new = cdev_lookup(inode->i_rdev);
+               if (!new)
                        return -ENXIO;
-               new = container_of(kobj, struct cdev, kobj);
                spin_lock(&cdev_lock);
                /* Check i_cdev again in case somebody beat us to it while
                   we dropped the lock. */
@@ -454,18 +472,6 @@ const struct file_operations def_chr_fops = {
        .llseek = noop_llseek,
 };
 
-static struct kobject *exact_match(dev_t dev, int *part, void *data)
-{
-       struct cdev *p = data;
-       return &p->kobj;
-}
-
-static int exact_lock(dev_t dev, void *data)
-{
-       struct cdev *p = data;
-       return cdev_get(p) ? 0 : -1;
-}
-
 /**
  * cdev_add() - add a char device to the system
  * @p: the cdev structure for the device
@@ -478,7 +484,7 @@ static int exact_lock(dev_t dev, void *data)
  */
 int cdev_add(struct cdev *p, dev_t dev, unsigned count)
 {
-       int error;
+       int error, i;
 
        p->dev = dev;
        p->count = count;
@@ -486,14 +492,22 @@ int cdev_add(struct cdev *p, dev_t dev, unsigned count)
        if (WARN_ON(dev == WHITEOUT_DEV))
                return -EBUSY;
 
-       error = kobj_map(cdev_map, dev, count, NULL,
-                        exact_match, exact_lock, p);
-       if (error)
-               return error;
+       mutex_lock(&chrdevs_lock);
+       for (i = 0; i < count; i++) {
+               error = xa_insert(&cdev_map, dev + i, p, GFP_KERNEL);
+               if (error)
+                       goto out_unwind;
+       }
+       mutex_unlock(&chrdevs_lock);
 
        kobject_get(p->kobj.parent);
-
        return 0;
+
+out_unwind:
+       while (--i >= 0)
+               xa_erase(&cdev_map, dev + i);
+       mutex_unlock(&chrdevs_lock);
+       return error;
 }
 
 /**
@@ -575,11 +589,6 @@ void cdev_device_del(struct cdev *cdev, struct device *dev)
                cdev_del(cdev);
 }
 
-static void cdev_unmap(dev_t dev, unsigned count)
-{
-       kobj_unmap(cdev_map, dev, count);
-}
-
 /**
  * cdev_del() - remove a cdev from the system
  * @p: the cdev structure to be removed
@@ -593,11 +602,16 @@ static void cdev_unmap(dev_t dev, unsigned count)
  */
 void cdev_del(struct cdev *p)
 {
-       cdev_unmap(p->dev, p->count);
+       int i;
+
+       mutex_lock(&chrdevs_lock);
+       for (i = 0; i < p->count; i++)
+               xa_erase(&cdev_map, p->dev + i);
+       mutex_unlock(&chrdevs_lock);
+
        kobject_put(&p->kobj);
 }
 
-
 static void cdev_default_release(struct kobject *kobj)
 {
        struct cdev *p = container_of(kobj, struct cdev, kobj);
@@ -656,20 +670,6 @@ void cdev_init(struct cdev *cdev, const struct 
file_operations *fops)
        cdev->ops = fops;
 }
 
-static struct kobject *base_probe(dev_t dev, int *part, void *data)
-{
-       if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
-               /* Make old-style 2.4 aliases work */
-               request_module("char-major-%d", MAJOR(dev));
-       return NULL;
-}
-
-void __init chrdev_init(void)
-{
-       cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
-}
-
-
 /* Let modules do char dev stuff */
 EXPORT_SYMBOL(register_chrdev_region);
 EXPORT_SYMBOL(unregister_chrdev_region);
diff --git a/fs/dcache.c b/fs/dcache.c
index ea0485861d9377..55e534ad6f8f7f 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -3233,5 +3233,4 @@ void __init vfs_caches_init(void)
        files_maxfiles_init();
        mnt_init();
        bdev_cache_init();
-       chrdev_init();
 }
diff --git a/fs/internal.h b/fs/internal.h
index 10517ece45167f..110e952e75a8aa 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -54,11 +54,6 @@ static inline void bd_forget(struct inode *inode)
 extern int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
                get_block_t *get_block, struct iomap *iomap);
 
-/*
- * char_dev.c
- */
-extern void __init chrdev_init(void);
-
 /*
  * fs_context.c
  */
-- 
2.28.0

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