[Devel] [RFC][PATCH 04/16] Use pid_to_nr() in process info functions

[sukadev at us.ibm.com]

Subject: Use pid_to_nr() in process info functions

From: Sukadev Bhattiprolu <sukadev at us.ibm.com>

Use pid_to_nr() function in getppid(), getpgid() and getsid() functions
so they return the correct pid_t for processes in multiple pid namespaces.

Note: We don't need pid_to_nr() in getpid() because the process always
     "sees itself" as being in its active pid namespace. Using pid_to_nr()
     in getpid() would unnecessarily hurt its performance.

Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
---
 include/linux/sched.h |   24 ++++++++++++++++++++++++
 kernel/sys.c          |   10 +++++-----
 kernel/timer.c        |    2 +-
 3 files changed, 30 insertions(+), 6 deletions(-)

Index: lx26-21-mm2/include/linux/sched.h
===================================================================
--- lx26-21-mm2.orig/include/linux/sched.h	2007-05-22 16:58:38.000000000 -0700
+++ lx26-21-mm2/include/linux/sched.h	2007-05-22 16:59:44.000000000 -0700
@@ -1124,6 +1124,30 @@ static inline struct pid *task_tgid(stru
 	return task->group_leader->pids[PIDTYPE_PID].pid;
 }
 
+/* NOTE: Caller must hold rcu_readlock() */
+static inline struct pid *task_parent_tgid(struct task_struct *task)
+{
+	return task_tgid(rcu_dereference(task->real_parent));
+}
+
+/* NOTE: Caller must hold rcu_readlock() */
+static inline struct pid *task_parent_pid(struct task_struct *task)
+{
+	return task_pid(rcu_dereference(task->real_parent));
+}
+
+/* NOTE: Caller must hold rcu_readlock() */
+static inline struct pid *task_tracer_tgid(struct task_struct *task)
+{
+	return task_tgid(rcu_dereference(task->parent));
+}
+
+/* NOTE: Caller must hold rcu_readlock() */
+static inline struct pid *task_tracer_pid(struct task_struct *task)
+{
+	return task_pid(rcu_dereference(task->parent));
+}
+
 static inline struct pid *task_pgrp(struct task_struct *task)
 {
 	return task->group_leader->pids[PIDTYPE_PGID].pid;
Index: lx26-21-mm2/kernel/timer.c
===================================================================
--- lx26-21-mm2.orig/kernel/timer.c	2007-05-22 16:58:38.000000000 -0700
+++ lx26-21-mm2/kernel/timer.c	2007-05-22 16:59:44.000000000 -0700
@@ -945,7 +945,7 @@ asmlinkage long sys_getppid(void)
 	int pid;
 
 	rcu_read_lock();
-	pid = rcu_dereference(current->real_parent)->tgid;
+	pid = pid_to_nr(task_parent_tgid(current));
 	rcu_read_unlock();
 
 	return pid;
Index: lx26-21-mm2/kernel/sys.c
===================================================================
--- lx26-21-mm2.orig/kernel/sys.c	2007-05-22 16:58:38.000000000 -0700
+++ lx26-21-mm2/kernel/sys.c	2007-05-22 16:59:44.000000000 -0700
@@ -1500,7 +1500,7 @@ out:
 asmlinkage long sys_getpgid(pid_t pid)
 {
 	if (!pid)
-		return process_group(current);
+		return pid_to_nr(task_pgrp(current));
 	else {
 		int retval;
 		struct task_struct *p;
@@ -1512,7 +1512,7 @@ asmlinkage long sys_getpgid(pid_t pid)
 		if (p) {
 			retval = security_task_getpgid(p);
 			if (!retval)
-				retval = process_group(p);
+				retval = pid_to_nr(task_pgrp(p));
 		}
 		read_unlock(&tasklist_lock);
 		return retval;
@@ -1524,7 +1524,7 @@ asmlinkage long sys_getpgid(pid_t pid)
 asmlinkage long sys_getpgrp(void)
 {
 	/* SMP - assuming writes are word atomic this is fine */
-	return process_group(current);
+	return pid_to_nr(task_pgrp(current));
 }
 
 #endif
@@ -1532,7 +1532,7 @@ asmlinkage long sys_getpgrp(void)
 asmlinkage long sys_getsid(pid_t pid)
 {
 	if (!pid)
-		return process_session(current);
+		return pid_to_nr(task_session(current));
 	else {
 		int retval;
 		struct task_struct *p;
@@ -1544,7 +1544,7 @@ asmlinkage long sys_getsid(pid_t pid)
 		if (p) {
 			retval = security_task_getsid(p);
 			if (!retval)
-				retval = process_session(p);
+				retval = pid_to_nr(task_session(p));
 		}
 		read_unlock(&tasklist_lock);
 		return retval;
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