[Devel] Re: [RFC][PATCH 0/15] Pid namespaces

[sukadev at us.ibm.com]

sukadev at us.ibm.com [sukadev at us.ibm.com] wrote:
| Pavel,
| 
| We seem to have a memory leak. Its new in this patchset (i.e the
| following test ran fine on the 2.6.22-rc6-mm1 patchset).
| 
| To repro: run "pidns_exec ./mypid" in a tight-loop  - where mypid.c
| is:
| 
| #include <stdio.h>
| #include <unistd.h>
| 
| main()
| {
|         printf("Pid %d, Ppid %d, Pgid %d, Sid %d\n",
|                  getpid(), getppid(), getpgid(0), getsid(0));
| }
| 
| I ran into OOM in about 30 mins. I am still investigating.
| 
| BTW, can we include a simple test program like the pidns_exec in this
| patch-0 for whoever want to play with pidns ?
| 
| Suka
| 

I think the problem is in create_pid_namespace(). kref_init() sets the
refcount to 1 and then we do a get_pid_ns() which sets it to 2.

free_nsproxy() frees one of this references, but the other is never
freed.

This patch seems to fix the leak. The patch also creates a slab cache
for the pid_namespace

---

Create a slab-cache for 'struct pid_namespace' and fix a memory leak
due to an extra reference in create_pid_namespace().

---
 kernel/pid.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Index: lx26-23-rc1-mm1/kernel/pid.c
===================================================================
--- lx26-23-rc1-mm1.orig/kernel/pid.c	2007-07-26 20:08:16.000000000 -0700
+++ lx26-23-rc1-mm1/kernel/pid.c	2007-07-26 22:31:42.000000000 -0700
@@ -35,6 +35,7 @@
 static struct hlist_head *pid_hash;
 static int pidhash_shift;
 struct pid init_struct_pid = INIT_STRUCT_PID;
+static struct kmem_cache *pid_ns_cachep;
 
 int pid_max = PID_MAX_DEFAULT;
 
@@ -525,7 +526,7 @@ static struct pid_namespace *create_pid_
 	struct pid_namespace *ns;
 	int i;
 
-	ns = kmalloc(sizeof(struct pid_namespace), GFP_KERNEL);
+	ns = kmem_cache_alloc(pid_ns_cachep, GFP_KERNEL);
 	if (ns == NULL)
 		goto out;
 
@@ -544,7 +545,6 @@ static struct pid_namespace *create_pid_
 
 	set_bit(0, ns->pidmap[0].page);
 	atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
-	get_pid_ns(ns);
 
 	for (i = 1; i < PIDMAP_ENTRIES; i++) {
 		ns->pidmap[i].page = 0;
@@ -556,7 +556,7 @@ static struct pid_namespace *create_pid_
 out_free_map:
 	kfree(ns->pidmap[0].page);
 out_free:
-	kfree(ns);
+	kmem_cache_free(pid_ns_cachep, ns);
 out:
 	return ERR_PTR(-ENOMEM);
 }
@@ -567,7 +567,7 @@ static void destroy_pid_namespace(struct
 
 	for (i = 0; i < PIDMAP_ENTRIES; i++)
 		kfree(ns->pidmap[i].page);
-	kfree(ns);
+	kmem_cache_free(pid_ns_cachep, ns);
 }
 
   struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *old_ns)
@@ -687,4 +687,6 @@ void __init pidmap_init(void)
 	init_pid_ns.pid_cachep = create_pid_cachep(1);
 	if (init_pid_ns.pid_cachep == NULL)
 		panic("Can't create pid_1 cachep\n");
+
+	pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
 }
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