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Date: Fri, 18 Jun 2010 23:23:55 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
Pavel Emelyanov <xemul@...nvz.org>,
Linux Containers <containers@...ts.osdl.org>,
linux-kernel@...r.kernel.org,
Louis Rilling <louis.rilling@...labs.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] procfs: Do not release pid_ns->proc_mnt too early
On 06/18, Oleg Nesterov wrote:
>
> work->func(ns) is
> called when ns is already fixed.
^^^^^
(I meant freed)
We can move kmem_cache_free(ns) into work->func(), or we can optimize
the usage of schedule_work(), something like the patch below.
Once again, it is completely untested, I do not pretend I understand
this code today, and I am sure the patch is wrong. I only try to discuss
the idea to break the circular reference. In any case, I am not proud
of this patch ;)
Or we should do the more sophisticated change suggested by Pavel. But
I'd like to avoid the changes in do_wait/release_task, this doesn't
look right to me.
Oleg.
include/linux/pid_namespace.h | 1 +
kernel/pid_namespace.c | 35 ++++++++++++++++++++++++++++++++++-
fs/proc/base.c | 4 ----
fs/proc/root.c | 10 ++++++----
4 files changed, 41 insertions(+), 9 deletions(-)
--- 34-rc1/include/linux/pid_namespace.h~PID_NS 2010-06-18 17:48:56.000000000 +0200
+++ 34-rc1/include/linux/pid_namespace.h 2010-06-18 22:37:45.000000000 +0200
@@ -26,6 +26,7 @@ struct pid_namespace {
struct pid_namespace *parent;
#ifdef CONFIG_PROC_FS
struct vfsmount *proc_mnt;
+ struct list_head dead_node;
#endif
#ifdef CONFIG_BSD_PROCESS_ACCT
struct bsd_acct_struct *bacct;
--- 34-rc1/kernel/pid_namespace.c~PID_NS 2010-06-18 17:48:56.000000000 +0200
+++ 34-rc1/kernel/pid_namespace.c 2010-06-18 22:52:41.000000000 +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>
@@ -105,15 +106,47 @@ out:
return ERR_PTR(-ENOMEM);
}
-static void destroy_pid_namespace(struct pid_namespace *ns)
+static LIST_HEAD(dead_list);
+static DEFINE_SPINLOCK(dead_lock);
+
+static void do_destroy_pid_namespace(struct pid_namespace *ns)
{
int i;
+ pid_ns_release_proc(ns);
+
for (i = 0; i < PIDMAP_ENTRIES; i++)
kfree(ns->pidmap[i].page);
kmem_cache_free(pid_ns_cachep, ns);
}
+static void dead_work_func(struct work_struct *unused)
+{
+ LIST_HEAD(list);
+ unsigned long flags;
+ struct pid_namespace *ns, *tmp;
+
+ spin_lock_irqsave(&dead_lock, flags);
+ list_splice_init(&dead_list, &list);
+ spin_unlock_irqrestore(&dead_lock, flags);
+
+ list_for_each_entry_safe(ns, tmp, &list, dead_node)
+ do_destroy_pid_namespace(ns);
+}
+
+static DECLARE_WORK(dead_work, dead_work_func);
+
+static void destroy_pid_namespace(struct pid_namespace *ns)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&dead_lock, flags);
+ list_add(&ns->dead_node, &dead_list);
+ spin_unlock_irqrestore(&dead_lock, flags);
+
+ schedule_work(&dead_work);
+}
+
struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *old_ns)
{
if (!(flags & CLONE_NEWPID))
--- 34-rc1/fs/proc/base.c~PID_NS 2010-06-18 17:48:56.000000000 +0200
+++ 34-rc1/fs/proc/base.c 2010-06-18 17:49:45.000000000 +0200
@@ -2720,10 +2720,6 @@ void proc_flush_task(struct task_struct
proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
tgid->numbers[i].nr);
}
-
- upid = &pid->numbers[pid->level];
- if (upid->nr == 1)
- pid_ns_release_proc(upid->ns);
}
static struct dentry *proc_pid_instantiate(struct inode *dir,
--- 34-rc1/fs/proc/root.c~PID_NS 2010-06-18 17:48:56.000000000 +0200
+++ 34-rc1/fs/proc/root.c 2010-06-18 22:54:03.000000000 +0200
@@ -31,7 +31,7 @@ static int proc_set_super(struct super_b
struct pid_namespace *ns;
ns = (struct pid_namespace *)data;
- sb->s_fs_info = get_pid_ns(ns);
+ sb->s_fs_info = ns;
return set_anon_super(sb, NULL);
}
@@ -74,7 +74,7 @@ static int proc_get_sb(struct file_syste
ei = PROC_I(sb->s_root->d_inode);
if (!ei->pid) {
rcu_read_lock();
- ei->pid = get_pid(find_pid_ns(1, ns));
+ ei->pid = find_pid_ns(1, ns);
rcu_read_unlock();
}
@@ -92,7 +92,6 @@ static void proc_kill_sb(struct super_bl
ns = (struct pid_namespace *)sb->s_fs_info;
kill_anon_super(sb);
- put_pid_ns(ns);
}
static struct file_system_type proc_fs_type = {
@@ -218,5 +217,8 @@ int pid_ns_prepare_proc(struct pid_names
void pid_ns_release_proc(struct pid_namespace *ns)
{
- mntput(ns->proc_mnt);
+ if (ns->proc_mnt) {
+ PROC_I(ns->proc_mnt->mnt_sb->s_root->d_inode)->pid = NULL;
+ mntput(ns->proc_mnt);
+ }
}
--
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