[Devel] Re: [PATCH 1/5] Define and use task_active_pid_ns() wrapper

[sukadev at us.ibm.com]

Serge E. Hallyn [serue at us.ibm.com] wrote:
| Quoting sukadev at us.ibm.com (sukadev at us.ibm.com):
| > 
| > Subject: [PATCH 1/5] Define and use task_active_pid_ns() wrapper
| > 
| > From: Sukadev Bhattiprolu <sukadev at us.ibm.com>
| > 
| > With multiple pid namespaces, a process is known by some pid_t in
| > every ancestor pid namespace.  Every time the process forks, the
| > child process also gets a pid_t in every ancestor pid namespace.
| > 
| > While a process is visible in >=1 pid namespaces, it can see pid_t's
| > in only one pid namespace.  We call this pid namespace it's "active
| > pid namespace", and it is always the youngest pid namespace in which
| > the process is known.
| > 
| > This patch defines and uses a wrapper to find the active pid namespace
| > of a process. The implementation of the wrapper will be changed in 
| > when support for multiple pid namespaces are added.
| > 
| > Changelog:
| > 	2.6.22-rc4-mm2-pidns1:
| > 	- [Pavel Emelianov, Alexey Dobriyan] Back out the change to use
| > 	  task_active_pid_ns() in child_reaper() since task->nsproxy
| > 	  can be NULL during task exit (so child_reaper() continues to
| > 	  use init_pid_ns).
| > 
| > 	  to implement child_reaper() since init_pid_ns.child_reaper to
| > 	  implement child_reaper() since tsk->nsproxy can be NULL during exit.
| > 
| > 	2.6.21-rc6-mm1:
| > 	- Rename task_pid_ns() to task_active_pid_ns() to reflect that a
| > 	  process can have multiple pid namespaces.
| > 
| > Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
| > Acked-by: Pavel Emelianov <xemul at openvz.org>
| > 
| > Cc: Eric W. Biederman <ebiederm at xmission.com>
| > Cc: Cedric Le Goater <clg at fr.ibm.com>
| > Cc: Dave Hansen <haveblue at us.ibm.com>
| > Cc: Serge Hallyn <serue at us.ibm.com>
| > Cc: Herbert Poetzel <herbert at 13thfloor.at>
| > ---
| >  fs/exec.c                     |    2 +-
| >  fs/proc/proc_misc.c           |    3 ++-
| >  include/linux/pid_namespace.h |    7 ++++++-
| >  kernel/exit.c                 |    5 +++--
| >  kernel/nsproxy.c              |    2 +-
| >  kernel/pid.c                  |    4 ++--
| >  6 files changed, 15 insertions(+), 8 deletions(-)
| > 
| > Index: lx26-22-rc6-mm1/include/linux/pid_namespace.h
| > ===================================================================
| > --- lx26-22-rc6-mm1.orig/include/linux/pid_namespace.h	2007-07-13 13:07:01.000000000 -0700
| > +++ lx26-22-rc6-mm1/include/linux/pid_namespace.h	2007-07-13 18:22:49.000000000 -0700
| > @@ -20,7 +20,7 @@ struct pid_namespace {
| >  	struct pidmap pidmap[PIDMAP_ENTRIES];
| >  	int last_pid;
| >  	struct task_struct *child_reaper;
| > -	struct kmem_cache_t *pid_cachep;
| > +	struct kmem_cache *pid_cachep;
| 
| This change is, of course, unrelated to the description.

Yes. It fixes a warning.

I had sent a mail earlier to this list about the warning, but I guess
that mail did not make it due to our mail server being down on Fri/Sat.

| 
| >  };
| > 
| >  extern struct pid_namespace init_pid_ns;
| > @@ -39,6 +39,11 @@ static inline void put_pid_ns(struct pid
| >  	kref_put(&ns->kref, free_pid_ns);
| >  }
| > 
| > +static inline struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
| > +{
| > +	return tsk->nsproxy->pid_ns;
| > +}
| > +
| 
| I trust you've tested this for the NFS oops?

The NFS problem we got was when exit_task_namespaces() and
exit_notify() were swapped in do_exit(). That change was in
a separate patch and Pavel's has a fix for it. 

And that patch is not in -mm yet I think.

This patch is a simple short-cut to what the mainline code is
already doing.

| 
| Taking the pid_ns out of the nsproxy was the trigger for the original
| bug, right, to which the solutions were to either take it from struct
| pid, or, so long as pid namespaces couldn't yet be unshared, use
| init_pid_ns?
| 
| thanks,
| -serge
| 
| >  static inline struct task_struct *child_reaper(struct task_struct *tsk)
| >  {
| >  	return init_pid_ns.child_reaper;
| > Index: lx26-22-rc6-mm1/fs/exec.c
| > ===================================================================
| > --- lx26-22-rc6-mm1.orig/fs/exec.c	2007-07-13 13:05:38.000000000 -0700
| > +++ lx26-22-rc6-mm1/fs/exec.c	2007-07-13 18:13:39.000000000 -0700
| > @@ -827,7 +827,7 @@ static int de_thread(struct task_struct 
| >  	 * so it is safe to do it under read_lock.
| >  	 */
| >  	if (unlikely(tsk->group_leader == child_reaper(tsk)))
| > -		tsk->nsproxy->pid_ns->child_reaper = tsk;
| > +		task_active_pid_ns(tsk)->child_reaper = tsk;
| > 
| >  	zap_other_threads(tsk);
| >  	read_unlock(&tasklist_lock);
| > Index: lx26-22-rc6-mm1/fs/proc/proc_misc.c
| > ===================================================================
| > --- lx26-22-rc6-mm1.orig/fs/proc/proc_misc.c	2007-07-13 13:05:38.000000000 -0700
| > +++ lx26-22-rc6-mm1/fs/proc/proc_misc.c	2007-07-13 13:07:48.000000000 -0700
| > @@ -94,7 +94,8 @@ static int loadavg_read_proc(char *page,
| >  		LOAD_INT(a), LOAD_FRAC(a),
| >  		LOAD_INT(b), LOAD_FRAC(b),
| >  		LOAD_INT(c), LOAD_FRAC(c),
| > -		nr_running(), nr_threads, current->nsproxy->pid_ns->last_pid);
| > +		nr_running(), nr_threads,
| > +		task_active_pid_ns(current)->last_pid);
| >  	return proc_calc_metrics(page, start, off, count, eof, len);
| >  }
| > 
| > Index: lx26-22-rc6-mm1/kernel/exit.c
| > ===================================================================
| > --- lx26-22-rc6-mm1.orig/kernel/exit.c	2007-07-13 13:06:52.000000000 -0700
| > +++ lx26-22-rc6-mm1/kernel/exit.c	2007-07-13 18:13:39.000000000 -0700
| > @@ -909,8 +909,9 @@ fastcall NORET_TYPE void do_exit(long co
| >  	if (unlikely(!tsk->pid))
| >  		panic("Attempted to kill the idle task!");
| >  	if (unlikely(tsk == child_reaper(tsk))) {
| > -		if (tsk->nsproxy->pid_ns != &init_pid_ns)
| > -			tsk->nsproxy->pid_ns->child_reaper = init_pid_ns.child_reaper;
| > +		if (task_active_pid_ns(tsk) != &init_pid_ns)
| > +			task_active_pid_ns(tsk)->child_reaper =
| > +					init_pid_ns.child_reaper;
| >  		else
| >  			panic("Attempted to kill init!");
| >  	}
| > Index: lx26-22-rc6-mm1/kernel/pid.c
| > ===================================================================
| > --- lx26-22-rc6-mm1.orig/kernel/pid.c	2007-07-13 13:07:01.000000000 -0700
| > +++ lx26-22-rc6-mm1/kernel/pid.c	2007-07-13 18:13:38.000000000 -0700
| > @@ -214,7 +214,7 @@ struct pid *alloc_pid(void)
| >  	int nr = -1;
| >  	struct pid_namespace *ns;
| > 
| > -	ns = current->nsproxy->pid_ns;
| > +	ns = task_active_pid_ns(current);
| >  	pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
| >  	if (!pid)
| >  		goto out;
| > @@ -364,7 +364,7 @@ struct pid *find_ge_pid(int nr)
| >  		pid = find_pid(nr);
| >  		if (pid)
| >  			break;
| > -		nr = next_pidmap(current->nsproxy->pid_ns, nr);
| > +		nr = next_pidmap(task_active_pid_ns(current), nr);
| >  	} while (nr > 0);
| > 
| >  	return pid;
| > Index: lx26-22-rc6-mm1/kernel/nsproxy.c
| > ===================================================================
| > --- lx26-22-rc6-mm1.orig/kernel/nsproxy.c	2007-07-13 13:05:38.000000000 -0700
| > +++ lx26-22-rc6-mm1/kernel/nsproxy.c	2007-07-13 13:07:48.000000000 -0700
| > @@ -86,7 +86,7 @@ static struct nsproxy *create_new_namesp
| >  		goto out_ipc;
| >  	}
| > 
| > -	new_nsp->pid_ns = copy_pid_ns(flags, tsk->nsproxy->pid_ns);
| > +	new_nsp->pid_ns = copy_pid_ns(flags, task_active_pid_ns(tsk));
| >  	if (IS_ERR(new_nsp->pid_ns)) {
| >  		err = PTR_ERR(new_nsp->pid_ns);
| >  		goto out_pid;
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