[PATCH] proc: Remove tasklist_lock from proc_task_readdir.

This is just like my previous removal of tasklist_lock from first_tgid, and
next_tgid.  It simply had to wait until it was rcu safe to walk the thread
list.

This should be the last instance of the tasklist_lock in proc.  So user
processes should not be able to influence the tasklist lock hold times.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 773469703c62..6092a6e2c5a9 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2224,11 +2224,12 @@ int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
  * In the case of a seek we start with the leader and walk nr
  * threads past it.
  */
-static struct task_struct *first_tid(struct task_struct *leader, int tid, int nr)
+static struct task_struct *first_tid(struct task_struct *leader,
+                                        int tid, int nr)
 {
         struct task_struct *pos = NULL;
-        read_lock(&tasklist_lock);
 
+        rcu_read_lock();
         /* Attempt to start with the pid of a thread */
         if (tid && (nr > 0)) {
                 pos = find_task_by_pid(tid);
@@ -2258,7 +2259,7 @@ static struct task_struct *first_tid(struct task_struct *leader, int tid, int nr
         }
         pos = NULL;
 done:
-        read_unlock(&tasklist_lock);
+        rcu_read_unlock();
         return pos;
 }
 
@@ -2271,7 +2272,7 @@ done:
 static struct task_struct *next_tid(struct task_struct *start)
 {
         struct task_struct *pos;
-        read_lock(&tasklist_lock);
+        rcu_read_lock();
         pos = start;
         if (pid_alive(start))
                 pos = next_thread(start);
@@ -2279,7 +2280,7 @@ static struct task_struct *next_tid(struct task_struct *start)
                 get_task_struct(pos);
         else
                 pos = NULL;
-        read_unlock(&tasklist_lock);
+        rcu_read_unlock();
         put_task_struct(start);
         return pos;
 }