attach_pid() with struct pid parameter

attach_pid() currently takes a pid_t and then uses find_pid() to find the
corresponding struct pid.  Sometimes we already have the struct pid.  We can
then skip find_pid() if attach_pid() were to take a struct pid parameter.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: <containers@lists.osdl.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -702,7 +702,7 @@ static int de_thread(struct task_struct *tsk)
 		 */
 		detach_pid(tsk, PIDTYPE_PID);
 		tsk->pid = leader->pid;
-		attach_pid(tsk, PIDTYPE_PID,  tsk->pid);
+		attach_pid(tsk, PIDTYPE_PID,  find_pid(tsk->pid));
 		transfer_pid(leader, tsk, PIDTYPE_PGID);
 		transfer_pid(leader, tsk, PIDTYPE_SID);
 		list_replace_rcu(&leader->tasks, &tsk->tasks);

include/linux/pid.h

@@ -76,8 +76,7 @@ extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
  * write-held.
  */
 extern int FASTCALL(attach_pid(struct task_struct *task,
-				enum pid_type type, int nr));
-
+				enum pid_type type, struct pid *pid));
 extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
 extern void FASTCALL(transfer_pid(struct task_struct *old,
 				  struct task_struct *new, enum pid_type));

kernel/exit.c

@@ -302,12 +302,12 @@ void __set_special_pids(pid_t session, pid_t pgrp)
 	if (process_session(curr) != session) {
 		detach_pid(curr, PIDTYPE_SID);
 		set_signal_session(curr->signal, session);
-		attach_pid(curr, PIDTYPE_SID, session);
+		attach_pid(curr, PIDTYPE_SID, find_pid(session));
 	}
 	if (process_group(curr) != pgrp) {
 		detach_pid(curr, PIDTYPE_PGID);
 		curr->signal->pgrp = pgrp;
-		attach_pid(curr, PIDTYPE_PGID, pgrp);
+		attach_pid(curr, PIDTYPE_PGID, find_pid(pgrp));
 	}
 }
 

kernel/fork.c

@@ -1249,16 +1249,19 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 			__ptrace_link(p, current->parent);
 
 		if (thread_group_leader(p)) {
+			pid_t pgid = process_group(current);
+			pid_t sid = process_session(current);
+
 			p->signal->tty = current->signal->tty;
-			p->signal->pgrp = process_group(current);
+			p->signal->pgrp = pgid;
 			set_signal_session(p->signal, process_session(current));
-			attach_pid(p, PIDTYPE_PGID, process_group(p));
-			attach_pid(p, PIDTYPE_SID, process_session(p));
+			attach_pid(p, PIDTYPE_PGID, find_pid(pgid));
+			attach_pid(p, PIDTYPE_SID, find_pid(sid));
 
 			list_add_tail_rcu(&p->tasks, &init_task.tasks);
 			__get_cpu_var(process_counts)++;
 		}
-		attach_pid(p, PIDTYPE_PID, p->pid);
+		attach_pid(p, PIDTYPE_PID, find_pid(p->pid));
 		nr_threads++;
 	}
 

kernel/pid.c

@@ -247,13 +247,16 @@ struct pid * fastcall find_pid(int nr)
 }
 EXPORT_SYMBOL_GPL(find_pid);
 
-int fastcall attach_pid(struct task_struct *task, enum pid_type type, int nr)
+/*
+ * attach_pid() must be called with the tasklist_lock write-held.
+ */
+int fastcall attach_pid(struct task_struct *task, enum pid_type type,
+		struct pid *pid)
 {
 	struct pid_link *link;
-	struct pid *pid;
 
 	link = &task->pids[type];
-	link->pid = pid = find_pid(nr);
+	link->pid = pid;
 	hlist_add_head_rcu(&link->node, &pid->tasks[type]);
 
 	return 0;

kernel/sys.c

@@ -1488,7 +1488,7 @@ asmlinkage long sys_setpgid(pid_t pid, pid_t pgid)
 	if (process_group(p) != pgid) {
 		detach_pid(p, PIDTYPE_PGID);
 		p->signal->pgrp = pgid;
-		attach_pid(p, PIDTYPE_PGID, pgid);
+		attach_pid(p, PIDTYPE_PGID, find_pid(pgid));
 	}
 
 	err = 0;