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Subject[PATCH 3/3] pids: refactor vnr/nr_ns helpers to make them safe
Inho, the safety rules for vnr/nr_ns helpers are horrible and buggy.

task_pid_nr_ns(task) needs rcu/tasklist depending on task == current.

As for "special" pids, vnr/nr_ns helpers always need rcu. However,
if task != current, they are unsafe even under rcu lock, we can't
trust task->group_leader without the special checks.

And almost every helper has a callsite which needs a fix.

Also, it is a bit annoying that the implementations of, say,
task_pgrp_vnr() and task_pgrp_nr_ns() are not "symmetrical".

This patch introduces the new helper, __task_pid_nr_ns(), which is
always safe to use, and turns all other helpers into the trivial
wrappers.

If this patch is acceptable, I'll send another one which converts
task_tgid_xxx() as well, there are a bit special.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>

--- CUR/include/linux/sched.h~SP_3_NR 2009-01-16 02:13:50.000000000 +0100
+++ CUR/include/linux/sched.h 2009-01-16 04:16:12.000000000 +0100
@@ -1481,17 +1481,23 @@ struct pid_namespace;
*
* see also pid_nr() etc in include/linux/pid.h
*/
+pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
+ struct pid_namespace *ns);

static inline pid_t task_pid_nr(struct task_struct *tsk)
{
return tsk->pid;
}

-pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns);
+static inline pid_t task_pid_nr_ns(struct task_struct *tsk,
+ struct pid_namespace *ns)
+{
+ return __task_pid_nr_ns(tsk, PIDTYPE_PID, ns);
+}

static inline pid_t task_pid_vnr(struct task_struct *tsk)
{
- return pid_vnr(task_pid(tsk));
+ return __task_pid_nr_ns(tsk, PIDTYPE_PID, NULL);
}


@@ -1513,11 +1519,15 @@ static inline pid_t task_pgrp_nr(struct
return tsk->signal->__pgrp;
}

-pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns);
+static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk,
+ struct pid_namespace *ns)
+{
+ return __task_pid_nr_ns(tsk, PIDTYPE_PGID, ns);
+}

static inline pid_t task_pgrp_vnr(struct task_struct *tsk)
{
- return pid_vnr(task_pgrp(tsk));
+ return __task_pid_nr_ns(tsk, PIDTYPE_PGID, NULL);
}


@@ -1526,14 +1536,17 @@ static inline pid_t task_session_nr(stru
return tsk->signal->__session;
}

-pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns);
+static inline pid_t task_session_nr_ns(struct task_struct *tsk,
+ struct pid_namespace *ns)
+{
+ return __task_pid_nr_ns(tsk, PIDTYPE_SID, ns);
+}

static inline pid_t task_session_vnr(struct task_struct *tsk)
{
- return pid_vnr(task_session(tsk));
+ return __task_pid_nr_ns(tsk, PIDTYPE_SID, NULL);
}

-
/**
* pid_alive - check that a task structure is not stale
* @p: Task structure to be checked.
--- CUR/kernel/pid.c~SP_3_NR 2009-01-16 02:54:26.000000000 +0100
+++ CUR/kernel/pid.c 2009-01-16 05:40:43.000000000 +0100
@@ -452,11 +452,24 @@ pid_t pid_vnr(struct pid *pid)
}
EXPORT_SYMBOL_GPL(pid_vnr);

-pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
+pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
+ struct pid_namespace *ns)
{
- return pid_nr_ns(task_pid(tsk), ns);
+ pid_t nr = 0;
+
+ rcu_read_lock();
+ if (!ns)
+ ns = current->nsproxy->pid_ns;
+ if (likely(pid_alive(task))) {
+ if (type != PIDTYPE_PID)
+ task = task->group_leader;
+ nr = pid_nr_ns(task->pids[type].pid, ns);
+ }
+ rcu_read_unlock();
+
+ return nr;
}
-EXPORT_SYMBOL(task_pid_nr_ns);
+EXPORT_SYMBOL(__task_pid_nr_ns);

pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
{
@@ -464,18 +477,6 @@ pid_t task_tgid_nr_ns(struct task_struct
}
EXPORT_SYMBOL(task_tgid_nr_ns);

-pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
-{
- return pid_nr_ns(task_pgrp(tsk), ns);
-}
-EXPORT_SYMBOL(task_pgrp_nr_ns);
-
-pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
-{
- return pid_nr_ns(task_session(tsk), ns);
-}
-EXPORT_SYMBOL(task_session_nr_ns);
-
struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
{
return ns_of_pid(task_pid(tsk));


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