Isolate some explicit usage of task->tgid

With pid namespaces this field is now dangerous to use explicitly, so hide
it behind the helpers.

Also the pid and pgrp fields o task_struct and signal_struct are to be
deprecated.  Unfortunately this patch cannot be sent right now as this
leads to tons of warnings, so start isolating them, and deprecate later.

Actually the p->tgid == pid has to be changed to has_group_leader_pid(),
but Oleg pointed out that in case of posix cpu timers this is the same, and
thread_group_leader() is more preferable.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -841,8 +841,8 @@ static int de_thread(struct task_struct *tsk)
 		 */
 		tsk->start_time = leader->start_time;
 
-		BUG_ON(leader->tgid != tsk->tgid);
-		BUG_ON(tsk->pid == tsk->tgid);
+		BUG_ON(!same_thread_group(leader, tsk));
+		BUG_ON(has_group_leader_pid(tsk));
 		/*
 		 * An exec() starts a new thread group with the
 		 * TGID of the previous thread group. Rehash the

fs/proc/base.c

@@ -2553,7 +2553,7 @@ static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry
 	rcu_read_unlock();
 	if (!task)
 		goto out;
-	if (leader->tgid != task->tgid)
+	if (!same_thread_group(leader, task))
 		goto out_drop_task;
 
 	result = proc_task_instantiate(dir, dentry, task, NULL);

include/linux/sched.h

@@ -1725,6 +1725,12 @@ static inline int has_group_leader_pid(struct task_struct *p)
 	return p->pid == p->tgid;
 }
 
+static inline
+int same_thread_group(struct task_struct *p1, struct task_struct *p2)
+{
+	return p1->tgid == p2->tgid;
+}
+
 static inline struct task_struct *next_thread(const struct task_struct *p)
 {
 	return list_entry(rcu_dereference(p->thread_group.next),

kernel/posix-cpu-timers.c

@@ -21,8 +21,8 @@ static int check_clock(const clockid_t which_clock)
 
 	read_lock(&tasklist_lock);
 	p = find_task_by_pid(pid);
-	if (!p || (CPUCLOCK_PERTHREAD(which_clock) ?
-		   p->tgid != current->tgid : p->tgid != pid)) {
+	if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ?
+		   same_thread_group(p, current) : thread_group_leader(p))) {
 		error = -EINVAL;
 	}
 	read_unlock(&tasklist_lock);
@@ -308,13 +308,13 @@ int posix_cpu_clock_get(const clockid_t which_clock, struct timespec *tp)
 		p = find_task_by_pid(pid);
 		if (p) {
 			if (CPUCLOCK_PERTHREAD(which_clock)) {
-				if (p->tgid == current->tgid) {
+				if (same_thread_group(p, current)) {
 					error = cpu_clock_sample(which_clock,
 								 p, &rtn);
 				}
 			} else {
 				read_lock(&tasklist_lock);
-				if (p->tgid == pid && p->signal) {
+				if (thread_group_leader(p) && p->signal) {
 					error =
 					    cpu_clock_sample_group(which_clock,
 							           p, &rtn);
@@ -355,15 +355,15 @@ int posix_cpu_timer_create(struct k_itimer *new_timer)
 			p = current;
 		} else {
 			p = find_task_by_pid(pid);
-			if (p && p->tgid != current->tgid)
+			if (p && !same_thread_group(p, current))
 				p = NULL;
 		}
 	} else {
 		if (pid == 0) {
 			p = current->group_leader;
 		} else {
 			p = find_task_by_pid(pid);
-			if (p && p->tgid != pid)
+			if (p && !thread_group_leader(p))
 				p = NULL;
 		}
 	}

kernel/posix-timers.c

@@ -404,7 +404,7 @@ static struct task_struct * good_sigevent(sigevent_t * event)
 
 	if ((event->sigev_notify & SIGEV_THREAD_ID ) &&
 		(!(rtn = find_task_by_pid(event->sigev_notify_thread_id)) ||
-		 rtn->tgid != current->tgid ||
+		 !same_thread_group(rtn, current) ||
 		 (event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_SIGNAL))
 		return NULL;
 
@@ -608,7 +608,7 @@ static struct k_itimer * lock_timer(timer_t timer_id, unsigned long *flags)
 		spin_lock(&timr->it_lock);
 
 		if ((timr->it_id != timer_id) || !(timr->it_process) ||
-				timr->it_process->tgid != current->tgid) {
+				!same_thread_group(timr->it_process, current)) {
 			spin_unlock(&timr->it_lock);
 			spin_unlock_irqrestore(&idr_lock, *flags);
 			timr = NULL;

kernel/ptrace.c

@@ -169,7 +169,7 @@ int ptrace_attach(struct task_struct *task)
 	retval = -EPERM;
 	if (task->pid <= 1)
 		goto out;
-	if (task->tgid == current->tgid)
+	if (same_thread_group(task, current))
 		goto out;
 
 repeat:

kernel/signal.c

@@ -1150,7 +1150,7 @@ static int kill_something_info(int sig, struct siginfo *info, int pid)
 
 		read_lock(&tasklist_lock);
 		for_each_process(p) {
-			if (p->pid > 1 && p->tgid != current->tgid) {
+			if (p->pid > 1 && !same_thread_group(p, current)) {
 				int err = group_send_sig_info(sig, info, p);
 				++count;
 				if (err != -EPERM)

mm/oom_kill.c

@@ -326,7 +326,7 @@ static int oom_kill_task(struct task_struct *p)
 	 * to memory reserves though, otherwise we might deplete all memory.
 	 */
 	do_each_thread(g, q) {
-		if (q->mm == mm && q->tgid != p->tgid)
+		if (q->mm == mm && !same_thread_group(q, p))
 			force_sig(SIGKILL, q);
 	} while_each_thread(g, q);