ANDROID: uid_sys_stats: Replace tasklist lock with RCU in uid_cputime_show

Tasklist lock is acuquired in uid_cputime_show for updating the stats
for all tasks in the system. This can potentially disable preemption
for several milli seconds. Replace tasklist_lock with RCU read side
primitives.

Change-Id: Ife69cb577bfdceaae6eb21b9bda09a0fe687e140
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>

diff --git a/drivers/misc/uid_sys_stats.c b/drivers/misc/uid_sys_stats.c
index 0014ad5..a940f97 100644 (file)
--- a/drivers/misc/uid_sys_stats.c
+++ b/drivers/misc/uid_sys_stats.c
@@ -346,13 +346,13 @@ static int uid_cputime_show(struct seq_file *m, void *v)
                uid_entry->active_utime = 0;
        }
 
-       read_lock(&tasklist_lock);
+       rcu_read_lock();
        do_each_thread(temp, task) {
                uid = from_kuid_munged(user_ns, task_uid(task));
                if (!uid_entry || uid_entry->uid != uid)
                        uid_entry = find_or_register_uid(uid);
                if (!uid_entry) {
-                       read_unlock(&tasklist_lock);
+                       rcu_read_unlock();
                        rt_mutex_unlock(&uid_lock);
                        pr_err("%s: failed to find the uid_entry for uid %d\n",
                                __func__, uid);
@@ -362,7 +362,7 @@ static int uid_cputime_show(struct seq_file *m, void *v)
                uid_entry->active_utime += utime;
                uid_entry->active_stime += stime;
        } while_each_thread(temp, task);
-       read_unlock(&tasklist_lock);
+       rcu_read_unlock();
 
        hash_for_each(hash_table, bkt, uid_entry, hash) {
                cputime_t total_utime = uid_entry->utime +