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

[Pavel Emelyanov]

sukadev at us.ibm.com wrote:
> 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.

That's it! I've switched from my old fast (and bad) reference counting
scheme to new slow (and correct) one, but forgot to remove this "get".
This is the real problem. Thanks :)

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

OK, I'll include this patch. Thanks.

> ---
> 
> 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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