linux-kernel - [PATCH 3.2 56/94] pid: get pid_t ppid of task in init_pid

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Date:	Mon, 28 Apr 2014 02:11:22 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Richard Guy Briggs" <rgb@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 3.2 56/94] pid: get pid_t ppid of task in init_pid_ns

3.2.58-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Richard Guy Briggs <rgb@...hat.com>

commit ad36d28293936b03d6b7996e9d6aadfd73c0eb08 upstream.

Added the functions task_ppid_nr_ns() and task_ppid_nr() to abstract the lookup
of the PPID (real_parent's pid_t) of a process, including rcu locking, in the
arbitrary and init_pid_ns.
This provides an alternative to sys_getppid(), which is relative to the child
process' pid namespace.

(informed by ebiederman's 6c621b7e)
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 include/linux/sched.h | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1690,6 +1690,24 @@ static inline pid_t task_tgid_vnr(struct
 }
 
 
+static int pid_alive(const struct task_struct *p);
+static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
+{
+	pid_t pid = 0;
+
+	rcu_read_lock();
+	if (pid_alive(tsk))
+		pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);
+	rcu_read_unlock();
+
+	return pid;
+}
+
+static inline pid_t task_ppid_nr(const struct task_struct *tsk)
+{
+	return task_ppid_nr_ns(tsk, &init_pid_ns);
+}
+
 static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk,
 					struct pid_namespace *ns)
 {
@@ -1727,7 +1745,7 @@ static inline pid_t task_pgrp_nr(struct
  * If pid_alive fails, then pointers within the task structure
  * can be stale and must not be dereferenced.
  */
-static inline int pid_alive(struct task_struct *p)
+static inline int pid_alive(const struct task_struct *p)
 {
 	return p->pids[PIDTYPE_PID].pid != NULL;
 }

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