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Date: Fri, 16 Nov 2012 08:35:44 -0800
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: Linux Containers <containers@...ts.linux-foundation.org>
Cc: <linux-kernel@...r.kernel.org>, Oleg Nesterov <oleg@...sign.ru>,
Serge Hallyn <serge@...lyn.com>,
Gao feng <gaofeng@...fujitsu.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 05/11] pidns: Make the pidns proc mount/umount logic obvious.
From: "Eric W. Biederman" <ebiederm@...ssion.com>
Track the number of pids in the proc hash table. When the number of
pids goes to 0 schedule work to unmount the kernel mount of proc.
Move the mount of proc into alloc_pid when we allocate the pid for
init.
Remove the surprising calls of pid_ns_release proc in fork and
proc_flush_task. Those code paths really shouldn't know about proc
namespace implementation details and people have demonstrated several
times that finding and understanding those code paths is difficult and
non-obvious.
Because of the call path detach pid is alwasy called with the
rtnl_lock held free_pid is not allowed to sleep, so the work to
unmounting proc is moved to a work queue. This has the side benefit
of not blocking the entire world waiting for the unnecessary
rcu_barrier in deactivate_locked_super.
In the process of making the code clear and obvious this fixes a bug
reported by Gao feng <gaofeng@...fujitsu.com> where we would leak a
mount of proc during clone(CLONE_NEWPID|CLONE_NEWNET) if copy_pid_ns
succeeded and copy_net_ns failed.
Acked-by: "Serge E. Hallyn" <serge@...lyn.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
fs/proc/base.c | 4 ----
fs/proc/root.c | 5 -----
include/linux/pid_namespace.h | 2 ++
kernel/fork.c | 2 --
kernel/pid.c | 21 +++++++++++++++++----
kernel/pid_namespace.c | 14 +++++++-------
6 files changed, 26 insertions(+), 22 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 6177fc2..7621dc5 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2590,10 +2590,6 @@ void proc_flush_task(struct task_struct *task)
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,
diff --git a/fs/proc/root.c b/fs/proc/root.c
index fc16093..f2f2511 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -155,11 +155,6 @@ void __init proc_root_init(void)
err = register_filesystem(&proc_fs_type);
if (err)
return;
- err = pid_ns_prepare_proc(&init_pid_ns);
- if (err) {
- unregister_filesystem(&proc_fs_type);
- return;
- }
proc_self_init();
proc_symlink("mounts", NULL, "self/mounts");
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index c89c9cf..4c96acd 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -21,6 +21,7 @@ struct pid_namespace {
struct kref kref;
struct pidmap pidmap[PIDMAP_ENTRIES];
int last_pid;
+ int nr_hashed;
struct task_struct *child_reaper;
struct kmem_cache *pid_cachep;
unsigned int level;
@@ -32,6 +33,7 @@ struct pid_namespace {
struct bsd_acct_struct *bacct;
#endif
struct user_namespace *user_ns;
+ struct work_struct proc_work;
kgid_t pid_gid;
int hide_pid;
int reboot; /* group exit code if this pidns was rebooted */
diff --git a/kernel/fork.c b/kernel/fork.c
index 7798c24..666dc8b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1476,8 +1476,6 @@ bad_fork_cleanup_io:
if (p->io_context)
exit_io_context(p);
bad_fork_cleanup_namespaces:
- if (unlikely(clone_flags & CLONE_NEWPID))
- pid_ns_release_proc(p->nsproxy->pid_ns);
exit_task_namespaces(p);
bad_fork_cleanup_mm:
if (p->mm)
diff --git a/kernel/pid.c b/kernel/pid.c
index 3a5f238..e957f8b 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -36,6 +36,7 @@
#include <linux/pid_namespace.h>
#include <linux/init_task.h>
#include <linux/syscalls.h>
+#include <linux/proc_fs.h>
#define pid_hashfn(nr, ns) \
hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
@@ -270,8 +271,12 @@ void free_pid(struct pid *pid)
unsigned long flags;
spin_lock_irqsave(&pidmap_lock, flags);
- for (i = 0; i <= pid->level; i++)
- hlist_del_rcu(&pid->numbers[i].pid_chain);
+ for (i = 0; i <= pid->level; i++) {
+ struct upid *upid = pid->numbers + i;
+ hlist_del_rcu(&upid->pid_chain);
+ if (--upid->ns->nr_hashed == 0)
+ schedule_work(&upid->ns->proc_work);
+ }
spin_unlock_irqrestore(&pidmap_lock, flags);
for (i = 0; i <= pid->level; i++)
@@ -293,6 +298,7 @@ struct pid *alloc_pid(struct pid_namespace *ns)
goto out;
tmp = ns;
+ pid->level = ns->level;
for (i = ns->level; i >= 0; i--) {
nr = alloc_pidmap(tmp);
if (nr < 0)
@@ -303,17 +309,23 @@ struct pid *alloc_pid(struct pid_namespace *ns)
tmp = tmp->parent;
}
+ if (unlikely(is_child_reaper(pid))) {
+ if (pid_ns_prepare_proc(ns))
+ goto out_free;
+ }
+
get_pid_ns(ns);
- pid->level = ns->level;
atomic_set(&pid->count, 1);
for (type = 0; type < PIDTYPE_MAX; ++type)
INIT_HLIST_HEAD(&pid->tasks[type]);
upid = pid->numbers + ns->level;
spin_lock_irq(&pidmap_lock);
- for ( ; upid >= pid->numbers; --upid)
+ for ( ; upid >= pid->numbers; --upid) {
hlist_add_head_rcu(&upid->pid_chain,
&pid_hash[pid_hashfn(upid->nr, upid->ns)]);
+ upid->ns->nr_hashed++;
+ }
spin_unlock_irq(&pidmap_lock);
out:
@@ -570,6 +582,7 @@ void __init pidmap_init(void)
/* Reserve PID 0. We never call free_pidmap(0) */
set_bit(0, init_pid_ns.pidmap[0].page);
atomic_dec(&init_pid_ns.pidmap[0].nr_free);
+ init_pid_ns.nr_hashed = 1;
init_pid_ns.pid_cachep = KMEM_CACHE(pid,
SLAB_HWCACHE_ALIGN | SLAB_PANIC);
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 7580aa0..cc44db7 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -72,6 +72,12 @@ err_alloc:
return NULL;
}
+static void proc_cleanup_work(struct work_struct *work)
+{
+ struct pid_namespace *ns = container_of(work, struct pid_namespace, proc_work);
+ pid_ns_release_proc(ns);
+}
+
/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
#define MAX_PID_NS_LEVEL 32
@@ -105,6 +111,7 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
ns->level = level;
ns->parent = get_pid_ns(parent_pid_ns);
ns->user_ns = get_user_ns(user_ns);
+ INIT_WORK(&ns->proc_work, proc_cleanup_work);
set_bit(0, ns->pidmap[0].page);
atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
@@ -112,15 +119,8 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
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_pid_ns;
-
return ns;
-out_put_parent_pid_ns:
- put_pid_ns(parent_pid_ns);
- put_user_ns(user_ns);
out_free_map:
kfree(ns->pidmap[0].page);
out_free:
--
1.7.5.4
--
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