devcgroup: remove spin_lock()

Since we introduced rcu for read side, spin_lock is used only for update.
But we always hold cgroup_lock() when update, so spin_lock() is not need.

Additional cleanup:
1) include linux/rcupdate.h explicitly
2) remove unused variable cur_devcgroup in devcgroup_update_access()

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: "Serge E. Hallyn" <serue@us.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 29 deletions

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index d5c15a7c67c3..5ba78701adc3 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -1,5 +1,5 @@
 /*
- * dev_cgroup.c - device cgroup subsystem
+ * device_cgroup.c - device cgroup subsystem
  *
  * Copyright 2007 IBM Corp
  */
@@ -10,6 +10,7 @@
 #include <linux/list.h>
 #include <linux/uaccess.h>
 #include <linux/seq_file.h>
+#include <linux/rcupdate.h>
 
 #define ACC_MKNOD 1
 #define ACC_READ  2
@@ -22,18 +23,8 @@
 
 /*
  * whitelist locking rules:
- * cgroup_lock() cannot be taken under dev_cgroup->lock.
- * dev_cgroup->lock can be taken with or without cgroup_lock().
- *
- * modifications always require cgroup_lock
- * modifications to a list which is visible require the
- *   dev_cgroup->lock *and* cgroup_lock()
- * walking the list requires dev_cgroup->lock or cgroup_lock().
- *
- * reasoning: dev_whitelist_copy() needs to kmalloc, so needs
- *   a mutex, which the cgroup_lock() is.  Since modifying
- *   a visible list requires both locks, either lock can be
- *   taken for walking the list.
+ * hold cgroup_lock() for update/read.
+ * hold rcu_read_lock() for read.
  */
 
 struct dev_whitelist_item {
@@ -47,7 +38,6 @@ struct dev_whitelist_item {
 struct dev_cgroup {
         struct cgroup_subsys_state css;
         struct list_head whitelist;
-        spinlock_t lock;
 };
 
 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
@@ -103,7 +93,6 @@ free_and_exit:
 /* Stupid prototype - don't bother combining existing entries */
 /*
  * called under cgroup_lock()
- * since the list is visible to other tasks, we need the spinlock also
  */
 static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
                         struct dev_whitelist_item *wh)
@@ -114,7 +103,6 @@ static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
         if (!whcopy)
                 return -ENOMEM;
 
-        spin_lock(&dev_cgroup->lock);
         list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
                 if (walk->type != wh->type)
                         continue;
@@ -130,7 +118,6 @@ static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
 
         if (whcopy != NULL)
                 list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);
-        spin_unlock(&dev_cgroup->lock);
         return 0;
 }
 
@@ -144,14 +131,12 @@ static void whitelist_item_free(struct rcu_head *rcu)
 
 /*
  * called under cgroup_lock()
- * since the list is visible to other tasks, we need the spinlock also
  */
 static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
                         struct dev_whitelist_item *wh)
 {
         struct dev_whitelist_item *walk, *tmp;
 
-        spin_lock(&dev_cgroup->lock);
         list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
                 if (walk->type == DEV_ALL)
                         goto remove;
@@ -169,7 +154,6 @@ remove:
                         call_rcu(&walk->rcu, whitelist_item_free);
                 }
         }
-        spin_unlock(&dev_cgroup->lock);
 }
 
 /*
@@ -209,7 +193,6 @@ static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
                 }
         }
 
-        spin_lock_init(&dev_cgroup->lock);
         return &dev_cgroup->css;
 }
 
@@ -325,15 +308,11 @@ static int parent_has_perm(struct dev_cgroup *childcg,
 {
         struct cgroup *pcg = childcg->css.cgroup->parent;
         struct dev_cgroup *parent;
-        int ret;
 
         if (!pcg)
                 return 1;
         parent = cgroup_to_devcgroup(pcg);
-        spin_lock(&parent->lock);
-        ret = may_access_whitelist(parent, wh);
-        spin_unlock(&parent->lock);
-        return ret;
+        return may_access_whitelist(parent, wh);
 }
 
 /*
@@ -352,7 +331,6 @@ static int parent_has_perm(struct dev_cgroup *childcg,
 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
                                    int filetype, const char *buffer)
 {
-        struct dev_cgroup *cur_devcgroup;
         const char *b;
         char *endp;
         int count;
@@ -361,8 +339,6 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
         if (!capable(CAP_SYS_ADMIN))
                 return -EPERM;
 
-        cur_devcgroup = task_devcgroup(current);
-
         memset(&wh, 0, sizeof(wh));
         b = buffer;