[PATCH 14/38] tap: Convert minor_idr to XArray

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <wi...@infradead.org>

The minor_lock can be removed as the XArray contains its own spinlock.
I suspect the GFP_ATOMIC allocation could be GFP_KERNEL, but I couldn't
prove it.

Signed-off-by: Matthew Wilcox (Oracle) <wi...@infradead.org>
---
 drivers/net/tap.c | 32 +++++++++++++-------------------
 1 file changed, 13 insertions(+), 19 deletions(-)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index dd614c2cd994..81b06a21d96c 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -14,9 +14,9 @@
 #include <linux/slab.h>
 #include <linux/wait.h>
 #include <linux/cdev.h>
-#include <linux/idr.h>
 #include <linux/fs.h>
 #include <linux/uio.h>
+#include <linux/xarray.h>
 
 #include <net/net_namespace.h>
 #include <net/rtnetlink.h>
@@ -106,8 +106,7 @@ static LIST_HEAD(major_list);
 struct major_info {
        struct rcu_head rcu;
        dev_t major;
-       struct idr minor_idr;
-       spinlock_t minor_lock;
+       struct xarray tap_devs;
        const char *device_name;
        struct list_head next;
 };
@@ -414,19 +413,16 @@ int tap_get_minor(dev_t major, struct tap_dev *tap)
                goto unlock;
        }
 
-       spin_lock(&tap_major->minor_lock);
-       retval = idr_alloc(&tap_major->minor_idr, tap, 1, TAP_NUM_DEVS, 
GFP_ATOMIC);
-       if (retval >= 0) {
-               tap->minor = retval;
-       } else if (retval == -ENOSPC) {
+       retval = xa_alloc(&tap_major->tap_devs, &tap->minor, tap,
+                       XA_LIMIT(0, TAP_NUM_DEVS), GFP_ATOMIC);
+       if (retval == -EBUSY) {
                netdev_err(tap->dev, "Too many tap devices\n");
                retval = -EINVAL;
        }
-       spin_unlock(&tap_major->minor_lock);
 
 unlock:
        rcu_read_unlock();
-       return retval < 0 ? retval : 0;
+       return retval;
 }
 EXPORT_SYMBOL_GPL(tap_get_minor);
 
@@ -440,12 +436,12 @@ void tap_free_minor(dev_t major, struct tap_dev *tap)
                goto unlock;
        }
 
-       spin_lock(&tap_major->minor_lock);
+       xa_lock(&tap_major->tap_devs);
        if (tap->minor) {
-               idr_remove(&tap_major->minor_idr, tap->minor);
+               __xa_erase(&tap_major->tap_devs, tap->minor);
                tap->minor = 0;
        }
-       spin_unlock(&tap_major->minor_lock);
+       xa_unlock(&tap_major->tap_devs);
 
 unlock:
        rcu_read_unlock();
@@ -465,13 +461,13 @@ static struct tap_dev *dev_get_by_tap_file(int major, int 
minor)
                goto unlock;
        }
 
-       spin_lock(&tap_major->minor_lock);
-       tap = idr_find(&tap_major->minor_idr, minor);
+       xa_lock(&tap_major->tap_devs);
+       tap = xa_load(&tap_major->tap_devs, minor);
        if (tap) {
                dev = tap->dev;
                dev_hold(dev);
        }
-       spin_unlock(&tap_major->minor_lock);
+       xa_unlock(&tap_major->tap_devs);
 
 unlock:
        rcu_read_unlock();
@@ -1322,8 +1318,7 @@ static int tap_list_add(dev_t major, const char 
*device_name)
 
        tap_major->major = MAJOR(major);
 
-       idr_init(&tap_major->minor_idr);
-       spin_lock_init(&tap_major->minor_lock);
+       xa_init_flags(&tap_major->tap_devs, XA_FLAGS_ALLOC1);
 
        tap_major->device_name = device_name;
 
@@ -1369,7 +1364,6 @@ void tap_destroy_cdev(dev_t major, struct cdev *tap_cdev)
        unregister_chrdev_region(major, TAP_NUM_DEVS);
        list_for_each_entry_safe(tap_major, tmp, &major_list, next) {
                if (tap_major->major == MAJOR(major)) {
-                       idr_destroy(&tap_major->minor_idr);
                        list_del_rcu(&tap_major->next);
                        kfree_rcu(tap_major, rcu);
                }
-- 
2.23.0.rc1