sukadev@us.ibm.com wrote:
> Subject: Introduce proc_mnt for pid_ns
> 
> From: Dave Hansen <hansendc@us.ibm.com>
> 
> The following patch completes the removal of the global proc_mnt.
> It fetches the mnt on which to do dentry invalidations from the
> pid_namespace in which the task appears.
> 
> For now, there is only one pid namespace in mainline so this is
> straightforward.  In the -lxc tree we'll have to do something
> more complex.  The proc_flush_task() code takes a task, and
> needs to be able to find the corresponding proc superblocks on
> which that tasks's /proc/<pid> directories could appear.  We
> can tell in which pid namespaces a task appears, so I put a
> pointer from the pid namespace to the corresponding proc_mnt.
> 
> /proc currently has some special code to make sure that the root
> directory gets set up correctly.  It proc_mnt variable in order
> to find its way to the root inode.
> 
> Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
> Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> ---
> 
>  fs/proc/base.c                |   32 ++++++++++++++++++++++++-
>  fs/proc/inode.c               |   11 +++++++-
>  fs/proc/root.c                |   52 ++++++++++++++++++++++++++++--------------
>  include/linux/pid_namespace.h |    1 
>  include/linux/proc_fs.h       |    1 
>  5 files changed, 75 insertions(+), 22 deletions(-)
> 
> Index: lx26-21-mm2/fs/proc/base.c
> ===================================================================
> --- lx26-21-mm2.orig/fs/proc/base.c	2007-05-22 16:59:49.000000000 -0700
> +++ lx26-21-mm2/fs/proc/base.c	2007-05-22 16:59:56.000000000 -0700
> @@ -2005,9 +2005,11 @@ static const struct inode_operations pro
>  };
>  
>  /**
> - * proc_flush_task -  Remove dcache entries for @task from the /proc dcache.
> + * proc_flush_task_from_pid_ns -  Remove dcache entries for @task
> + * 				  from the /proc dcache.
>   *
>   * @task: task that should be flushed.
> + * @pid_ns: pid_namespace in which that task appears
>   *
>   * Looks in the dcache for
>   * /proc/@pid
> @@ -2025,11 +2027,22 @@ static const struct inode_operations pro
>   *       that no dcache entries will exist at process exit time it
>   *       just makes it very unlikely that any will persist.
>   */
> -void proc_flush_task(struct task_struct *task)
> +static void proc_flush_task_from_pid_ns(struct task_struct *task,
> +				struct pid_namespace* pid_ns)
>  {
>  	struct dentry *dentry, *leader, *dir;
>  	char buf[PROC_NUMBUF];
>  	struct qstr name;
> +	struct vfsmount *proc_mnt;
> +
> +	WARN_ON(!pid_ns);
> +	/*
> +	 * It is possible that no /procs have been instantiated
> +	 * for this particular pid namespace.
> +	 */
> +	if (!pid_ns->proc_mnt)
> +		return;
> +	proc_mnt = pid_ns->proc_mnt;
>  
>  	name.name = buf;
>  	name.len = snprintf(buf, sizeof(buf), "%d", task->pid);
> @@ -2071,6 +2084,21 @@ out:
>  	return;
>  }
>  
> +void proc_flush_task(struct task_struct *task)
> +{
> +	int i;
> +	struct pid *pid;
> +	struct upid* upid;
> +
> +	pid = task_pid(task);
> +	if (!pid)
> +		return;
> +
> +	upid = &pid->upid_list[0];
> +	for (i = 0; i < pid->num_upids; i++, upid++)
> +		proc_flush_task_from_pid_ns(task, upid->pid_ns);
> +}
> +
>  static struct dentry *proc_pid_instantiate(struct inode *dir,
>  					   struct dentry * dentry,
>  					   struct task_struct *task, const void *ptr)
> Index: lx26-21-mm2/fs/proc/inode.c
> ===================================================================
> --- lx26-21-mm2.orig/fs/proc/inode.c	2007-05-22 16:51:19.000000000 -0700
> +++ lx26-21-mm2/fs/proc/inode.c	2007-05-22 16:59:56.000000000 -0700
> @@ -6,6 +6,7 @@
>  
>  #include <linux/time.h>
>  #include <linux/proc_fs.h>
> +#include <linux/hardirq.h>
>  #include <linux/kernel.h>
>  #include <linux/mm.h>
>  #include <linux/string.h>
> @@ -74,8 +75,6 @@ static void proc_delete_inode(struct ino
>  	clear_inode(inode);
>  }
>  
> -struct vfsmount *proc_mnt;
> -
>  static void proc_read_inode(struct inode * inode)
>  {
>  	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
> @@ -458,6 +457,8 @@ out_mod:
>  
>  int proc_fill_super(struct super_block *s, void *data, int silent)
>  {
> +	struct pid_namespace *pid_ns = data;
> +	struct proc_inode *ei;
>  	struct inode * root_inode;
>  
>  	s->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC;
> @@ -466,6 +467,7 @@ int proc_fill_super(struct super_block *
>  	s->s_magic = PROC_SUPER_MAGIC;
>  	s->s_op = &proc_sops;
>  	s->s_time_gran = 1;
> +	s->s_fs_info = pid_ns;

This must be done in set callback for sget. Otherwise we
may have two superblocks with the same pid_ns...

>  	de_get(&proc_root);
>  	root_inode = proc_get_inode(s, PROC_ROOT_INO, &proc_root);
> @@ -476,6 +478,11 @@ int proc_fill_super(struct super_block *
>  	s->s_root = d_alloc_root(root_inode);
>  	if (!s->s_root)
>  		goto out_no_root;
> +	/* Seed the root directory with a pid so it doesn't need
> +	 * to be special in base.c.
> +	 */
> +	ei = PROC_I(root_inode);
> +	ei->pid = find_get_pid(1);
>  	return 0;
>  
>  out_no_root:
> Index: lx26-21-mm2/fs/proc/root.c
> ===================================================================
> --- lx26-21-mm2.orig/fs/proc/root.c	2007-05-22 16:51:19.000000000 -0700
> +++ lx26-21-mm2/fs/proc/root.c	2007-05-22 16:59:56.000000000 -0700
> @@ -12,32 +12,56 @@
>  #include <linux/time.h>
>  #include <linux/proc_fs.h>
>  #include <linux/stat.h>
> +#include <linux/hardirq.h>
>  #include <linux/init.h>
>  #include <linux/sched.h>
>  #include <linux/module.h>
>  #include <linux/bitops.h>
>  #include <linux/smp_lock.h>
>  #include <linux/mount.h>
> +#include <linux/pid_namespace.h>
>  
>  #include "internal.h"
>  
>  struct proc_dir_entry *proc_net, *proc_net_stat, *proc_bus, *proc_root_fs, *proc_root_driver;
>  
> +static int proc_test_sb(struct super_block *s, void *data)
> +{
> +	struct pid_namespace *pid_ns = data;
> +	if (s->s_fs_info == pid_ns)
> +		return 1;
> +	return 0;
> +}
> +
>  static int proc_get_sb(struct file_system_type *fs_type,
>  	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
>  {
> -	if (proc_mnt) {
> -		/* Seed the root directory with a pid so it doesn't need
> -		 * to be special in base.c.  I would do this earlier but
> -		 * the only task alive when /proc is mounted the first time
> -		 * is the init_task and it doesn't have any pids.
> -		 */
> -		struct proc_inode *ei;
> -		ei = PROC_I(proc_mnt->mnt_sb->s_root->d_inode);
> -		if (!ei->pid)
> -			ei->pid = find_get_pid(1);
> +	int error;
> +	struct super_block *s;
> +	struct pid_namespace *pid_ns;
> +
> +	/*
> +	 * We can eventually derive this out of whatever mount
> +	 * arguments the user supplies, but just take it from
> +	 * current for now.
> +	 */
> +	pid_ns = task_active_pid_ns(current);
> +
> +	s = sget(fs_type, proc_test_sb, set_anon_super, pid_ns);
> +	if (IS_ERR(s))
> +		return PTR_ERR(s);
> +
> +	error = proc_fill_super(s, pid_ns, 0);
> +	if (error) {
> +		deactivate_super(s);
> +		return error;
>  	}
> -	return get_sb_single(fs_type, flags, data, proc_fill_super, mnt);
> +
> +	if (!pid_ns->proc_mnt)
> +		pid_ns->proc_mnt = mnt;
> +
> +	do_remount_sb(s, flags, data, 0);
> +	return simple_set_mnt(mnt, s);
>  }
>  
>  static struct file_system_type proc_fs_type = {
> @@ -54,12 +78,6 @@ void __init proc_root_init(void)
>  	err = register_filesystem(&proc_fs_type);
>  	if (err)
>  		return;
> -	proc_mnt = kern_mount(&proc_fs_type);
> -	err = PTR_ERR(proc_mnt);
> -	if (IS_ERR(proc_mnt)) {
> -		unregister_filesystem(&proc_fs_type);
> -		return;
> -	}
>  	proc_misc_init();
>  	proc_net = proc_mkdir("net", NULL);
>  	proc_net_stat = proc_mkdir("net/stat", NULL);
> Index: lx26-21-mm2/include/linux/pid_namespace.h
> ===================================================================
> --- lx26-21-mm2.orig/include/linux/pid_namespace.h	2007-05-22 16:59:53.000000000 -0700
> +++ lx26-21-mm2/include/linux/pid_namespace.h	2007-05-22 16:59:56.000000000 -0700
> @@ -33,6 +33,7 @@ struct pid_namespace {
>  	int last_pid;
>  	struct task_struct *child_reaper;
>  	atomic_t terminating;
> +	struct vfsmount *proc_mnt;
>  };
>  
>  extern struct pid_namespace init_pid_ns;
> Index: lx26-21-mm2/include/linux/proc_fs.h
> ===================================================================
> --- lx26-21-mm2.orig/include/linux/proc_fs.h	2007-05-22 16:51:19.000000000 -0700
> +++ lx26-21-mm2/include/linux/proc_fs.h	2007-05-22 16:59:56.000000000 -0700
> @@ -125,7 +125,6 @@ extern struct proc_dir_entry *create_pro
>  						struct proc_dir_entry *parent);
>  extern void remove_proc_entry(const char *name, struct proc_dir_entry *parent);
>  
> -extern struct vfsmount *proc_mnt;
>  extern int proc_fill_super(struct super_block *,void *,int);
>  extern struct inode *proc_get_inode(struct super_block *, unsigned int, struct proc_dir_entry *);
>  
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