[PATCH] RCU signal handling

RCU tasklist_lock and RCU signal handling: send signals RCU-read-locked
instead of tasklist_lock read-locked.  This is a scalability improvement on
SMP and a preemption-latency improvement under PREEMPT_RCU.

Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: William Irwin <wli@holomorphy.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 11 insertions, 11 deletions

diff --git a/kernel/pid.c b/kernel/pid.c
index edba31c681ac..1acc07246991 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -136,7 +136,7 @@ struct pid * fastcall find_pid(enum pid_type type, int nr)
         struct hlist_node *elem;
         struct pid *pid;
 
-        hlist_for_each_entry(pid, elem,
+        hlist_for_each_entry_rcu(pid, elem,
                         &pid_hash[type][pid_hashfn(nr)], pid_chain) {
                 if (pid->nr == nr)
                         return pid;
@@ -150,15 +150,15 @@ int fastcall attach_pid(task_t *task, enum pid_type type, int nr)
 
         task_pid = &task->pids[type];
         pid = find_pid(type, nr);
+        task_pid->nr = nr;
         if (pid == NULL) {
-                hlist_add_head(&task_pid->pid_chain,
-                                &pid_hash[type][pid_hashfn(nr)]);
                 INIT_LIST_HEAD(&task_pid->pid_list);
+                hlist_add_head_rcu(&task_pid->pid_chain,
+                                   &pid_hash[type][pid_hashfn(nr)]);
         } else {
                 INIT_HLIST_NODE(&task_pid->pid_chain);
-                list_add_tail(&task_pid->pid_list, &pid->pid_list);
+                list_add_tail_rcu(&task_pid->pid_list, &pid->pid_list);
         }
-        task_pid->nr = nr;
 
         return 0;
 }
@@ -170,20 +170,20 @@ static fastcall int __detach_pid(task_t *task, enum pid_type type)
 
         pid = &task->pids[type];
         if (!hlist_unhashed(&pid->pid_chain)) {
-                hlist_del(&pid->pid_chain);
 
-                if (list_empty(&pid->pid_list))
+                if (list_empty(&pid->pid_list)) {
                         nr = pid->nr;
-                else {
+                        hlist_del_rcu(&pid->pid_chain);
+                } else {
                         pid_next = list_entry(pid->pid_list.next,
                                                 struct pid, pid_list);
                         /* insert next pid from pid_list to hash */
-                        hlist_add_head(&pid_next->pid_chain,
-                                &pid_hash[type][pid_hashfn(pid_next->nr)]);
+                        hlist_replace_rcu(&pid->pid_chain,
+                                          &pid_next->pid_chain);
                 }
         }
 
-        list_del(&pid->pid_list);
+        list_del_rcu(&pid->pid_list);
         pid->nr = 0;
 
         return nr;