Re: [PATCH] Isolate some explicit usage of task->tgid

[Pavel Emelyanov <xemul@openvz.org>]

Oleg Nesterov wrote:
> On 08/17, Pavel Emelyanov wrote:
>> Actually the p->tgid == pid has to be changed to has_group_leader_pid(), 
>> but Oleg pointed out that this is the same and thread_group_leader() 
>> is more preferable. 
> 
> No, no, sorry for confusion! I was not clear. I meant that thread_group_leader()
> is imho better for posix timers, but

Oh! Sorry, new patch is included:

From: Pavel Emelyanov <xemul@openvz.org>

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>

---

 fs/exec.c                 |    4 ++--
 fs/proc/base.c            |    2 +-
 include/linux/sched.h     |    6 ++++++
 kernel/posix-cpu-timers.c |   12 ++++++------
 kernel/posix-timers.c     |    4 ++--
 kernel/ptrace.c           |    2 +-
 kernel/signal.c           |    2 +-
 mm/oom_kill.c             |    2 +-
 8 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f8cebf8..24b669d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1691,6 +1691,12 @@ static inline int has_group_leader_pid(s
 	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),
diff --git a/fs/exec.c b/fs/exec.c
index 35013f2..796453b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -865,8 +865,8 @@ static int de_thread(struct task_struct 
 
 		write_lock_irq(&tasklist_lock);
 
-		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
diff --git a/fs/proc/base.c b/fs/proc/base.c
index e3009ab..6dce57c 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2474,7 +2474,7 @@ static struct dentry *proc_task_lookup(s
 	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);
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index b53c8fc..68c9637 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -21,8 +21,8 @@ static int check_clock(const clockid_t w
 
 	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 
 		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);
@@ -355,7 +355,7 @@ int posix_cpu_timer_create(struct k_itim
 			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 {
@@ -363,7 +363,7 @@ int posix_cpu_timer_create(struct k_itim
 			p = current->group_leader;
 		} else {
 			p = find_task_by_pid(pid);
-			if (p && p->tgid != pid)
+			if (p && !thread_group_leader(p))
 				p = NULL;
 		}
 	}
diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 8d2cb05..bc77ba8 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -404,7 +404,7 @@ static struct task_struct * good_sigeven
 
 	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;
 
@@ -609,7 +609,7 @@ static struct k_itimer * lock_timer(time
 		spin_unlock(&idr_lock);
 
 		if ((timr->it_id != timer_id) || !(timr->it_process) ||
-				timr->it_process->tgid != current->tgid) {
+				!same_thread_group(timr->it_process, current)) {
 			unlock_timer(timr, *flags);
 			timr = NULL;
 		}
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 0d7fd07..f90207a 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -169,7 +169,7 @@ int ptrace_attach(struct task_struct *ta
 	retval = -EPERM;
 	if (task->pid <= 1)
 		goto out;
-	if (task->tgid == current->tgid)
+	if (same_thread_group(task, current))
 		goto out;
 
 repeat:
diff --git a/kernel/signal.c b/kernel/signal.c
index d6ca591..df785a7 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1145,7 +1145,7 @@ static int kill_something_info(int sig, 
 
 		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)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index e276a3c..1a2f687 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -330,7 +330,7 @@ static int oom_kill_task(struct task_str
 	 * 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);