Subject: Re: net-next: NULL pointer dereference on adding a net namespace and a system freeze

From: Jakub Kiciński <[email-masked]>
Date: Mon, 10 Mar 2014 13:19:09 +0100

On Sun, 09 Mar 2014 21:09:17 -0700, Eric Dumazet wrote:
> On Sun, 2014-03-09 at 21:02 -0700, Eric Dumazet wrote:
> > On Mon, 2014-03-10 at 01:44 +0100, Jakub Kicinski wrote:
> > > Hi!
> > > 
> > > Running Fedora 20 with net-next I get the following warning when
> > > libvirt or rtkit comes up:
> > > 
> > > [  272.143488] kmem_cache_sanity_check (flow_cache): Cache name already exists.
> > > [  272.143586] CPU: 0 PID: 975 Comm: libvirtd Not tainted 3.14.0-rc5+ #1
> > > [  272.143589] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> > > [  272.143591]  0000000000000000 ffff88003ceadba0 ffffffff8167baf0 ffff88003db3d300
> > > [  272.143595]  ffff88003ceadc18 ffffffff8117795b ffff88003ceadbc8 ffff88003b235158
> > > [  272.143599]  0000000000000000 0000000000040000 0000000000000068 0000000000000000
> > > [  272.143602] Call Trace:
> > > [  272.143610]  [<ffffffff8167baf0>] dump_stack+0x4d/0x66
> > > [  272.143615]  [<ffffffff8117795b>] kmem_cache_create_memcg+0x12b/0x420
> > > [  272.143618]  [<ffffffff81177c7b>] kmem_cache_create+0x2b/0x30
> > > [  272.143622]  [<ffffffff815c4a0e>] flow_cache_init+0x2e/0x2b0
> > > [  272.143626]  [<ffffffff8164b017>] xfrm_net_init+0x227/0x360
> > > [  272.143629]  [<ffffffff8164af41>] ? xfrm_net_init+0x151/0x360
> > > [  272.143632]  [<ffffffff815a5921>] ops_init+0x41/0x150
> > > [  272.143635]  [<ffffffff815a5aa3>] setup_net+0x73/0x110
> > > [  272.143638]  [<ffffffff815a5fe2>] copy_net_ns+0x72/0x100
> > > [  272.143642]  [<ffffffff810943f9>] create_new_namespaces+0xf9/0x190
> > > [  272.143645]  [<ffffffff81094560>] copy_namespaces+0xd0/0xf0
> > > [  272.143648]  [<ffffffff81094495>] ? copy_namespaces+0x5/0xf0
> > > [  272.143651]  [<ffffffff81069be0>] copy_process.part.31+0x950/0x1b30
> > > [  272.143655]  [<ffffffff8106af95>] do_fork+0xd5/0x370
> > > [  272.143658]  [<ffffffff811c1b2d>] ? __fput+0x17d/0x240
> > > [  272.143662]  [<ffffffff8110440c>] ? __audit_syscall_entry+0x9c/0xf0
> > > [  272.143665]  [<ffffffff8106b2b6>] SyS_clone+0x16/0x20
> > > [  272.143669]  [<ffffffff8168cf19>] stub_clone+0x69/0x90
> > > [  272.143673]  [<ffffffff8168cb69>] ? system_call_fastpath+0x16/0x1b
> > > 
> > > 
> > > When I try to add a netns with 
> > > # ip netns add abcd
> > > I it dies with:
> > 
> > 
> > Yep, commit ca925cf1534ebcec332c08719a7dee6ee1782ce4 is buggy.
> > 
> >     flowcache: Make flow cache name space aware
> >     
> >     Inserting a entry into flowcache, or flushing flowcache should be based
> >     on per net scope. The reason to do so is flushing operation from fat
> >     netns crammed with flow entries will also making the slim netns with only
> >     a few flow cache entries go away in original implementation.
> >     
> >     Since flowcache is tightly coupled with IPsec, so it would be easier to
> >     put flow cache global parameters into xfrm namespace part. And one last
> >     thing needs to do is bumping flow cache genid, and flush flow cache should
> >     also be made in per net style.
> >     
> >     Signed-off-by: Fan Du <[email-masked]>
> >     Signed-off-by: Steffen Klassert <[email-masked]>
> > 
> > I fail to understand why the kmem_cache must be private to a netns.
> 
> Could you please try the following patch ?

It helps with the flow_cache warning and BUG ("ip netns add" works) but
machine still freezes after 5-10 minutes.  I will try to revert
ca925cf1534ebcec332c08719a7dee6ee1782ce4 and see if that solves it.

	-- kuba

> diff --git a/include/net/netns/xfrm.h b/include/net/netns/xfrm.h
> index 51f0dce7b643..3492434baf88 100644
> --- a/include/net/netns/xfrm.h
> +++ b/include/net/netns/xfrm.h
> @@ -64,7 +64,6 @@ struct netns_xfrm {
>  
>  	/* flow cache part */
>  	struct flow_cache	flow_cache_global;
> -	struct kmem_cache	*flow_cachep;
>  	atomic_t		flow_cache_genid;
>  	struct list_head	flow_cache_gc_list;
>  	spinlock_t		flow_cache_gc_lock;
> diff --git a/net/core/flow.c b/net/core/flow.c
> index 344a184011fd..102f8ea2eb6e 100644
> --- a/net/core/flow.c
> +++ b/net/core/flow.c
> @@ -45,6 +45,8 @@ struct flow_flush_info {
>  	struct completion		completion;
>  };
>  
> +static struct kmem_cache *flow_cachep __read_mostly;
> +
>  #define flow_cache_hash_size(cache)	(1 << (cache)->hash_shift)
>  #define FLOW_HASH_RND_PERIOD		(10 * 60 * HZ)
>  
> @@ -75,7 +77,7 @@ static void flow_entry_kill(struct flow_cache_entry *fle,
>  {
>  	if (fle->object)
>  		fle->object->ops->delete(fle->object);
> -	kmem_cache_free(xfrm->flow_cachep, fle);
> +	kmem_cache_free(flow_cachep, fle);
>  }
>  
>  static void flow_cache_gc_task(struct work_struct *work)
> @@ -230,7 +232,7 @@ flow_cache_lookup(struct net *net, const struct flowi *key, u16 family, u8 dir,
>  		if (fcp->hash_count > fc->high_watermark)
>  			flow_cache_shrink(fc, fcp);
>  
> -		fle = kmem_cache_alloc(net->xfrm.flow_cachep, GFP_ATOMIC);
> +		fle = kmem_cache_alloc(flow_cachep, GFP_ATOMIC);
>  		if (fle) {
>  			fle->net = net;
>  			fle->family = family;
> @@ -435,10 +437,10 @@ int flow_cache_init(struct net *net)
>  	int i;
>  	struct flow_cache *fc = &net->xfrm.flow_cache_global;
>  
> -	/* Initialize per-net flow cache global variables here */
> -	net->xfrm.flow_cachep = kmem_cache_create("flow_cache",
> -					sizeof(struct flow_cache_entry),
> -					0, SLAB_PANIC, NULL);
> +	if (!flow_cachep)
> +		flow_cachep = kmem_cache_create("flow_cache",
> +						sizeof(struct flow_cache_entry),
> +						0, SLAB_PANIC, NULL);
>  	spin_lock_init(&net->xfrm.flow_cache_gc_lock);
>  	INIT_LIST_HEAD(&net->xfrm.flow_cache_gc_list);
>  	INIT_WORK(&net->xfrm.flow_cache_gc_work, flow_cache_gc_task);
> 
> 
>