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From: Oleg Nesterov on 19 Jun 2010 15:20
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(a)redhat.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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Prev: [PATCH 1/4] procfs: proc_get_sb: consolidate/cleanup root_inode->pid logic
Next: [PATCH 0/4] pid_ns_prepare_proc/unshare cleanups