Eric W. Biederman [ebiederm@xmission.com] wrote:
| 
| A current problem with the pid namespace is that it is
| easy to do pid related work after exit_task_namespaces which
| drops the nsproxy pointer.
| 
| However if we are doing pid namespace related work we are
| always operating on some struct pid which retains the pid_namespace
| pointer of the pid namespace it was allocated in.
| 
| So provide ns_of_pid which allows us to find the pid
| namespace a pid was allocated in.
| 
| Using this we have the needed infrastructure to do pid
| namespace related work at anytime we have a struct pid,
| removing the chance of accidentally having a NULL
| pointer dereference when accessing current->nsproxy.

Yep.

| 
| Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
| ---
|  include/linux/pid.h |   11 +++++++++++
|  1 files changed, 11 insertions(+), 0 deletions(-)
| 
| diff --git a/include/linux/pid.h b/include/linux/pid.h
| index f84d532..c4b56c0 100644
| --- a/include/linux/pid.h
| +++ b/include/linux/pid.h
| @@ -123,6 +123,17 @@ int next_pidmap(struct pid_namespace *pid_ns, int last);
|  extern struct pid *alloc_pid(struct pid_namespace *ns);
|  extern void FASTCALL(free_pid(struct pid *pid));
| 
| +/* ns_of_pid returns the pid namespace in which the specified
| + * pid was allocated.
| + */
| +static inline struct pid_namespace *ns_of_pid(struct pid *pid)

My patch refers to this function as pid_active_pid_ns() - I have
been meaning to send that out on top of your signals patch.
Since a pid has many namespaces, we have been using 'active pid ns'
to refer to this ns.

Even your next patch modifies task_active_pid_ns() to use this.
So can we rename this functio to pid_active_pid_ns() ?

| +{
| +	struct pid_namespace *ns = NULL;
| +	if (pid)
| +		ns = pid->numbers[pid->level].ns;
| +	return ns;
| +}
| +
|  /*
|   * the helpers to get the pid's id seen from different namespaces
|   *
| -- 
| 1.5.3.rc6.17.g1911
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