linux-kernel - [PATCH 3/4] procfs: move pid_ns_prepare_proc() from copy_process() to create_pid

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Date:	Sat, 19 Jun 2010 21:10:56 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Louis Rilling <louis.rilling@...labs.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Linux Containers <containers@...ts.osdl.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/4] procfs: move pid_ns_prepare_proc() from copy_process()
	to create_pid_namespace()

Imho, pid_ns_prepare_proc() in copy_process() looks very ugly.

Now that pid_ns_prepare_proc()->proc_get_sb() does not depend on the
first alloc_pid(), we can move this code into create_pid_namespace().

This looks much more clean to me, and in theory more correct in case
we ever implement sys_unshare(CLONE_NEWPID).

Note: with or without this patch we have a bug. If CLONE_NEWPID fails
after pid_ns_prepare_proc(), nobody frees ns->proc_mnt. This will be
fixed by the next patches.

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

 kernel/fork.c          |    7 -------
 kernel/pid_namespace.c |   10 +++++++++-
 2 files changed, 9 insertions(+), 8 deletions(-)

--- 35-rc3/kernel/fork.c~PNS_3_KILL_FORK_MOUNT	2010-06-19 19:20:22.000000000 +0200
+++ 35-rc3/kernel/fork.c	2010-06-19 20:17:35.000000000 +0200
@@ -58,7 +58,6 @@
 #include <linux/taskstats_kern.h>
 #include <linux/random.h>
 #include <linux/tty.h>
-#include <linux/proc_fs.h>
 #include <linux/blkdev.h>
 #include <linux/fs_struct.h>
 #include <linux/magic.h>
@@ -1154,12 +1153,6 @@ static struct task_struct *copy_process(
 		pid = alloc_pid(p->nsproxy->pid_ns);
 		if (!pid)
 			goto bad_fork_cleanup_io;
-
-		if (clone_flags & CLONE_NEWPID) {
-			retval = pid_ns_prepare_proc(p->nsproxy->pid_ns);
-			if (retval < 0)
-				goto bad_fork_free_pid;
-		}
 	}
 
 	p->pid = pid_nr(pid);
--- 35-rc3/kernel/pid_namespace.c~PNS_3_KILL_FORK_MOUNT	2010-06-19 19:20:22.000000000 +0200
+++ 35-rc3/kernel/pid_namespace.c	2010-06-19 19:21:42.000000000 +0200
@@ -10,6 +10,7 @@
 
 #include <linux/pid.h>
 #include <linux/pid_namespace.h>
+#include <linux/proc_fs.h>
 #include <linux/syscalls.h>
 #include <linux/err.h>
 #include <linux/acct.h>
@@ -72,6 +73,7 @@ static struct pid_namespace *create_pid_
 {
 	struct pid_namespace *ns;
 	unsigned int level = parent_pid_ns->level + 1;
+	int err = -ENOMEM;
 	int i;
 
 	ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
@@ -96,14 +98,20 @@ static struct pid_namespace *create_pid_
 	for (i = 1; i < PIDMAP_ENTRIES; i++)
 		atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
 
+	err = pid_ns_prepare_proc(ns);
+	if (err)
+		goto out_put_parent;
+
 	return ns;
 
+out_put_parent:
+	put_pid_ns(parent_pid_ns);
 out_free_map:
 	kfree(ns->pidmap[0].page);
 out_free:
 	kmem_cache_free(pid_ns_cachep, ns);
 out:
-	return ERR_PTR(-ENOMEM);
+	return ERR_PTR(err);
 }
 
 static void destroy_pid_namespace(struct pid_namespace *ns)

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