pids: Compute task_tgid using signal->leader_pid

The cost is the the same and this removes the need
to worry about complications that come from de_thread
and group_leader changing.

__task_pid_nr_ns has been updated to take advantage of this change.
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

arch/ia64/kernel/asm-offsets.c

@@ -50,7 +50,6 @@ void foo(void)
 
 	DEFINE(IA64_TASK_BLOCKED_OFFSET,offsetof (struct task_struct, blocked));
 	DEFINE(IA64_TASK_CLEAR_CHILD_TID_OFFSET,offsetof (struct task_struct, clear_child_tid));
-	DEFINE(IA64_TASK_GROUP_LEADER_OFFSET, offsetof (struct task_struct, group_leader));
 	DEFINE(IA64_TASK_TGIDLINK_OFFSET, offsetof (struct task_struct, pids[PIDTYPE_PID].pid));
 	DEFINE(IA64_PID_LEVEL_OFFSET, offsetof (struct pid, level));
 	DEFINE(IA64_PID_UPID_OFFSET, offsetof (struct pid, numbers[0]));
@@ -68,6 +67,7 @@ void foo(void)
 	DEFINE(IA64_SIGNAL_GROUP_STOP_COUNT_OFFSET,offsetof (struct signal_struct,
 							     group_stop_count));
 	DEFINE(IA64_SIGNAL_SHARED_PENDING_OFFSET,offsetof (struct signal_struct, shared_pending));
+	DEFINE(IA64_SIGNAL_LEADER_PID_OFFSET, offsetof (struct signal_struct, leader_pid));
 
 	BLANK();
 

arch/ia64/kernel/fsys.S

@@ -62,16 +62,16 @@ ENTRY(fsys_getpid)
 	.prologue
 	.altrp b6
 	.body
-	add r17=IA64_TASK_GROUP_LEADER_OFFSET,r16
+	add r17=IA64_TASK_SIGNAL_OFFSET,r16
 	;;
-	ld8 r17=[r17]				// r17 = current->group_leader
+	ld8 r17=[r17]				// r17 = current->signal
 	add r9=TI_FLAGS+IA64_TASK_SIZE,r16
 	;;
 	ld4 r9=[r9]
-	add r17=IA64_TASK_TGIDLINK_OFFSET,r17
+	add r17=IA64_SIGNAL_LEADER_PID_OFFSET,r17
 	;;
 	and r9=TIF_ALLWORK_MASK,r9
-	ld8 r17=[r17]				// r17 = current->group_leader->pids[PIDTYPE_PID].pid
+	ld8 r17=[r17]				// r17 = current->signal->leader_pid
 	;;
 	add r8=IA64_PID_LEVEL_OFFSET,r17
 	;;

drivers/platform/x86/thinkpad_acpi.c

@@ -57,6 +57,7 @@
 #include <linux/list.h>
 #include <linux/mutex.h>
 #include <linux/sched.h>
+#include <linux/sched/signal.h>
 #include <linux/kthread.h>
 #include <linux/freezer.h>
 #include <linux/delay.h>

fs/fuse/file.c

@@ -12,6 +12,7 @@
 #include <linux/slab.h>
 #include <linux/kernel.h>
 #include <linux/sched.h>
+#include <linux/sched/signal.h>
 #include <linux/module.h>
 #include <linux/compat.h>
 #include <linux/swap.h>

fs/notify/fanotify/fanotify.c

@@ -8,6 +8,7 @@
 #include <linux/mount.h>
 #include <linux/sched.h>
 #include <linux/sched/user.h>
+#include <linux/sched/signal.h>
 #include <linux/types.h>
 #include <linux/wait.h>
 #include <linux/audit.h>

include/linux/sched.h

@@ -1202,11 +1202,6 @@ static inline struct pid *task_pid(struct task_struct *task)
 	return task->pids[PIDTYPE_PID].pid;
 }
 
-static inline struct pid *task_tgid(struct task_struct *task)
-{
-	return task->group_leader->pids[PIDTYPE_PID].pid;
-}
-
 /*
  * Without tasklist or RCU lock it is not safe to dereference
  * the result of task_pgrp/task_session even if task == current,

include/linux/sched/signal.h

@@ -564,6 +564,11 @@ struct pid *task_pid_type(struct task_struct *task, enum pid_type type)
 	return task->pids[type].pid;
 }
 
+static inline struct pid *task_tgid(struct task_struct *task)
+{
+	return task->signal->leader_pid;
+}
+
 static inline int get_nr_threads(struct task_struct *tsk)
 {
 	return tsk->signal->nr_threads;

include/net/scm.h

@@ -8,6 +8,7 @@
 #include <linux/security.h>
 #include <linux/pid.h>
 #include <linux/nsproxy.h>
+#include <linux/sched/signal.h>
 
 /* Well, we should have at least one descriptor open
  * to accept passed FDs 8)

kernel/pid.c

@@ -421,13 +421,14 @@ pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
 	if (!ns)
 		ns = task_active_pid_ns(current);
 	if (likely(pid_alive(task))) {
-		if (type != PIDTYPE_PID) {
-			if (type == __PIDTYPE_TGID)
-				type = PIDTYPE_PID;
-
-			task = task->group_leader;
-		}
-		nr = pid_nr_ns(rcu_dereference(task->pids[type].pid), ns);
+		struct pid *pid;
+		if (type == PIDTYPE_PID)
+			pid = task_pid(task);
+		else if (type == __PIDTYPE_TGID)
+			pid = task_tgid(task);
+		else
+			pid = rcu_dereference(task->group_leader->pids[type].pid);
+		nr = pid_nr_ns(pid, ns);
 	}
 	rcu_read_unlock();