Pavel Emelianov [xemul@openvz.org] wrote:
| sukadev@us.ibm.com wrote:
| > Subject: Move alloc_pid call to copy_process
| > 
| > From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
| > 
| > Move alloc_pid() into copy_process(). This will keep all pid and pid
| > namespace code together and simplify error handling when we support
| > multiple pid namespaces.
| 
| I haven't found this in patches, so I ask it here:
| 
| We clone a new task with CLONE_NEWPIDS flag. This task
| allocates its PIDTYPE_PID pid and this pid happens in 
| booth parent and child namespace. This is OK.

| Then new task attaches PIDTYPE_SID and PIDTYPE_PGID pids from
| parent task. But these ones are in parent namespace only. 
| 
| Right? Is that good?
| 

In this patch, yes, we still attach to the parent process, bc at this
point we still support only one namespace.

In the patch that actually allows creating multiple namespaces,
(Patch #11), I have the following code which makes the process
that cloned its pid ns a session and pgrp leader, just like
/sbin/init for init_pid_ns.

@@ -1255,11 +1254,17 @@ static struct task_struct *copy_process(
                        __ptrace_link(p, current->parent);

                if (thread_group_leader(p)) {
+                       struct pid *pgrp = task_pgrp(current);
+                       struct pid *session = task_session(current);
+
+                       if (clone_flags & CLONE_NEWPID)
+                               pgrp = session = pid;
+
                        p->signal->tty = current->signal->tty;
-                       p->signal->pgrp = process_group(current);
-                       set_signal_session(p->signal, process_session(current));
-                       attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
-                       attach_pid(p, PIDTYPE_SID, task_session(current));
+                       p->signal->pgrp = pid_to_nr(pgrp);
+                       set_signal_session(p->signal, pid_to_nr(session));
+                       attach_pid(p, PIDTYPE_PGID, pgrp);
+                       attach_pid(p, PIDTYPE_SID, session);

                        list_add_tail_rcu(&p->tasks, &init_task.tasks);
                        __get_cpu_var(process_counts)++;

| > Changelog: 
| > 	- [Eric Biederman] Move the check of copy_process_type to alloc_pid()/
| > 	  free_pid() and to avoid clutter in copy_process().
| > 
| > Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
| > ---
| >  include/linux/pid.h |    7 ++++++-
| >  kernel/fork.c       |   21 +++++++++++++--------
| >  kernel/pid.c        |   10 +++++++++-
| >  3 files changed, 28 insertions(+), 10 deletions(-)
| > 
| > Index: lx26-21-mm2/include/linux/pid.h
| > ===================================================================
| > --- lx26-21-mm2.orig/include/linux/pid.h	2007-05-22 16:59:40.000000000 -0700
| > +++ lx26-21-mm2/include/linux/pid.h	2007-05-22 17:06:48.000000000 -0700
| > @@ -3,6 +3,11 @@
| >  
| >  #include <linux/rcupdate.h>
| >  
| > +enum copy_process_type {
| > +	COPY_NON_IDLE_PROCESS,
| > +	COPY_IDLE_PROCESS,
| > +};
| > +
| >  enum pid_type
| >  {
| >  	PIDTYPE_PID,
| > @@ -95,7 +100,7 @@ extern struct pid *FASTCALL(find_pid(int
| >  extern struct pid *find_get_pid(int nr);
| >  extern struct pid *find_ge_pid(int nr);
| >  
| > -extern struct pid *alloc_pid(void);
| > +extern struct pid *alloc_pid(enum copy_process_type);
| >  extern void FASTCALL(free_pid(struct pid *pid));
| >  
| >  static inline pid_t pid_to_nr(struct pid *pid)
| > Index: lx26-21-mm2/kernel/fork.c
| > ===================================================================
| > --- lx26-21-mm2.orig/kernel/fork.c	2007-05-22 16:59:41.000000000 -0700
| > +++ lx26-21-mm2/kernel/fork.c	2007-05-22 17:06:48.000000000 -0700
| > @@ -961,10 +961,11 @@ static struct task_struct *copy_process(
| >  					unsigned long stack_size,
| >  					int __user *parent_tidptr,
| >  					int __user *child_tidptr,
| > -					struct pid *pid)
| > +					enum copy_process_type copy_src)
| >  {
| >  	int retval;
| >  	struct task_struct *p = NULL;
| > +	struct pid *pid;
| >  
| >  	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
| >  		return ERR_PTR(-EINVAL);
| > @@ -1025,6 +1026,10 @@ static struct task_struct *copy_process(
| >  	if (p->binfmt && !try_module_get(p->binfmt->module))
| >  		goto bad_fork_cleanup_put_domain;
| >  
| > +	pid = alloc_pid(copy_src);
| > +	if (!pid)
| > +		goto bad_fork_put_binfmt_module;
| > +
| >  	p->did_exec = 0;
| >  	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
| >  	copy_flags(clone_flags, p);
| > @@ -1305,6 +1310,8 @@ bad_fork_cleanup_cpuset:
| >  #endif
| >  	cpuset_exit(p);
| >  	delayacct_tsk_free(p);
| > +	free_pid(pid);
| > +bad_fork_put_binfmt_module:
| >  	if (p->binfmt)
| >  		module_put(p->binfmt->module);
| >  bad_fork_cleanup_put_domain:
| > @@ -1331,7 +1338,7 @@ struct task_struct * __cpuinit fork_idle
| >  	struct pt_regs regs;
| >  
| >  	task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL, NULL,
| > -				&init_struct_pid);
| > +				COPY_IDLE_PROCESS);
| >  	if (!IS_ERR(task))
| >  		init_idle(task, cpu);
| >  
| > @@ -1369,19 +1376,16 @@ long do_fork(unsigned long clone_flags,
| >  {
| >  	struct task_struct *p;
| >  	int trace = 0;
| > -	struct pid *pid = alloc_pid();
| >  	long nr;
| >  
| > -	if (!pid)
| > -		return -EAGAIN;
| > -	nr = pid->nr;
| >  	if (unlikely(current->ptrace)) {
| >  		trace = fork_traceflag (clone_flags);
| >  		if (trace)
| >  			clone_flags |= CLONE_PTRACE;
| >  	}
| >  
| > -	p = copy_process(clone_flags, stack_start, regs, stack_size, parent_tidptr, child_tidptr, pid);
| > +	p = copy_process(clone_flags, stack_start, regs, stack_size,
| > +			parent_tidptr, child_tidptr, COPY_NON_IDLE_PROCESS);
| >  	/*
| >  	 * Do this prior waking up the new thread - the thread pointer
| >  	 * might get invalid after that point, if the thread exits quickly.
| > @@ -1389,6 +1393,8 @@ long do_fork(unsigned long clone_flags,
| >  	if (!IS_ERR(p)) {
| >  		struct completion vfork;
| >  
| > +		nr = pid_to_nr(task_pid(p));
| > +
| >  		if (clone_flags & CLONE_VFORK) {
| >  			p->vfork_done = &vfork;
| >  			init_completion(&vfork);
| > @@ -1422,7 +1428,6 @@ long do_fork(unsigned long clone_flags,
| >  			}
| >  		}
| >  	} else {
| > -		free_pid(pid);
| >  		nr = PTR_ERR(p);
| >  	}
| >  	return nr;
| > Index: lx26-21-mm2/kernel/pid.c
| > ===================================================================
| > --- lx26-21-mm2.orig/kernel/pid.c	2007-05-22 16:59:46.000000000 -0700
| > +++ lx26-21-mm2/kernel/pid.c	2007-05-22 17:06:48.000000000 -0700
| > @@ -216,6 +216,10 @@ fastcall void free_pid(struct pid *pid)
| >  	/* We can be called with write_lock_irq(&tasklist_lock) held */
| >  	unsigned long flags;
| >  
| > +	/* check this here to keep copy_process() cleaner */
| > +	if (unlikely(pid == &init_struct_pid))
| > +		return;
| > +
| >  	spin_lock_irqsave(&pidmap_lock, flags);
| >  	hlist_del_rcu(&pid->pid_chain);
| >  	spin_unlock_irqrestore(&pidmap_lock, flags);
| > @@ -224,12 +228,16 @@ fastcall void free_pid(struct pid *pid)
| >  	call_rcu(&pid->rcu, delayed_put_pid);
| >  }
| >  
| > -struct pid *alloc_pid(void)
| > +struct pid *alloc_pid(enum copy_process_type copy_src)
| >  {
| >  	struct pid *pid;
| >  	enum pid_type type;
| >  	int nr = -1;
| >  
| > +	/* check this here to keep copy_process() cleaner */
| > +	if (unlikely(copy_src == COPY_IDLE_PROCESS))
| > +		return &init_struct_pid;
| > +
| >  	pid = kmem_cache_alloc(pid_cachep, GFP_KERNEL);
| >  	if (!pid)
| >  		goto out;
| > _______________________________________________
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| > 
| > _______________________________________________
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| > 
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