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Date: Wed, 04 Sep 2019 12:50:32 -0600
From: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
Sean Tranchetti <stranche@...eaurora.org>
Subject: Re: [PATCH net] dev: Delay the free of the percpu refcount
On 2019-08-30 15:03, Subash Abhinov Kasiviswanathan wrote:
>> This looks bogus.
>>
>> Whatever layer tries to access dev refcnt after free_netdev() has been
>> called is buggy.
>>
>> I would rather trap early and fix the root cause.
>>
>> Untested patch :
>>
>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>> index b5d28dadf964..8080f1305417 100644
>> --- a/include/linux/netdevice.h
>> +++ b/include/linux/netdevice.h
>> @@ -3723,6 +3723,7 @@ void netdev_run_todo(void);
>> */
>> static inline void dev_put(struct net_device *dev)
>> {
>> + BUG_ON(!dev->pcpu_refcnt);
>> this_cpu_dec(*dev->pcpu_refcnt);
>> }
>>
>> @@ -3734,6 +3735,7 @@ static inline void dev_put(struct net_device
>> *dev)
>> */
>> static inline void dev_hold(struct net_device *dev)
>> {
>> + BUG_ON(!dev->pcpu_refcnt);
>> this_cpu_inc(*dev->pcpu_refcnt);
>> }
>
> Hello Eric
>
> I am seeing a similar crash with your patch as well.
> The NULL dev->pcpu_refcnt was caught by the BUG you added.
>
> 786.510217: <6> kernel BUG at include/linux/netdevice.h:3633!
> 786.510263: <2> pc : in_dev_finish_destroy+0xcc/0xd0
> 786.510267: <2> lr : in_dev_finish_destroy+0x2c/0xd0
> 786.511220: <2> Call trace:
> 786.511225: <2> in_dev_finish_destroy+0xcc/0xd0
> 786.511230: <2> in_dev_rcu_put+0x24/0x30
> 786.511237: <2> rcu_nocb_kthread+0x43c/0x468
> 786.511243: <2> kthread+0x118/0x128
> 786.511249: <2> ret_from_fork+0x10/0x1c
>
> This seems to be happening when there is an allocation failure
> in the IPv6 notifier callback only.
>
> I had added some additional debug to narrow down the refcount
> validity along the callers of the dev_put/dev_hold.
> refcnt valid below shows that the pointer dev->pcpu_refcnt is valid
> while refcnt null shows the case where dev->pcpu_refcnt is NULL.
> The last dev_put happens after free_netdev leading to the
> dev->pcpu_refcnt to be accessed when NULL.
>
> 309.908501: <6> dev_hold() ffffffe13c9df000 ip6_vti0 refcnt valid
> setup_net+0xa0/0x210 -> ops_init+0x88/0x110
> 309.908674: <6> dev_hold() ffffffe13c9df000 ip6_vti0 refcnt valid
> register_netdevice+0x29c/0x5b0 -> netdev_register_kobject+0xd8/0x150
> 309.908696: <6> dev_hold() ffffffe13c9df000 ip6_vti0 refcnt valid
> register_netdevice+0x29c/0x5b0 -> netdev_register_kobject+0x100/0x150
> 309.908717: <6> dev_hold() ffffffe13c9df000 ip6_vti0 refcnt valid
> vti6_init_net+0x188/0x1c0 -> register_netdev+0x28/0x40
> 309.908763: <6> neighbour: dev_hold() ffffffe13c9df000 ip6_vti0
> refcnt valid inetdev_event+0x43c/0x528 -> inetdev_init+0x80/0x1e0
> 309.908835: <6> dev_hold() ffffffe13c9df000 ip6_vti0 refcnt valid
> raw_notifier_call_chain+0x3c/0x68 -> inetdev_event+0x43c/0x528
> 309.908882: <6> neighbour: dev_hold() ffffffe13c9df000 ip6_vti0
> refcnt valid addrconf_notify+0x42c/0xe58 -> ipv6_add_dev+0xe4/0x588
> 309.908890: <6> IPv6: dev_hold() ffffffe13c9df000 ip6_vti0 refcnt
> valid raw_notifier_call_chain+0x3c/0x68 -> addrconf_notify+0x42c/0xe58
> 309.908906: <6> stress-ng-clone: page allocation failure: order:0,
> mode:0x6040c0(GFP_KERNEL|__GFP_COMP), nodemask=(null)
> 309.908910: <6> stress-ng-clone cpuset=foreground mems_allowed=0
> 309.908925: <2> Call trace:
> 309.908931: <2> dump_backtrace+0x0/0x158
> 309.908934: <2> show_stack+0x14/0x20
> 309.908939: <2> dump_stack+0xc4/0xfc
> 309.908944: <2> warn_alloc+0xf8/0x168
> 309.908947: <2> __alloc_pages_nodemask+0xff4/0x1018
> 309.908955: <2> new_slab+0x128/0x5b8
> 309.908958: <2> ___slab_alloc+0x4cc/0x5f8
> 309.908960: <2> kmem_cache_alloc_trace+0x2a4/0x2c0
> 309.908963: <2> ipv6_add_dev+0x220/0x588
> 309.908966: <2> addrconf_notify+0x42c/0xe58
> 309.908969: <2> raw_notifier_call_chain+0x3c/0x68
> 309.908972: <2> register_netdevice+0x3c4/0x5b0
> 309.908974: <2> register_netdev+0x28/0x40
> 309.908978: <2> vti6_init_net+0x188/0x1c0
> 309.908981: <2> ops_init+0x88/0x110
> 309.908983: <2> setup_net+0xa0/0x210
> 309.908986: <2> copy_net_ns+0xa8/0x130
> 309.908990: <2> create_new_namespaces+0x138/0x170
> 309.908993: <2> unshare_nsproxy_namespaces+0x68/0x90
> 309.908999: <2> ksys_unshare+0x17c/0x248
> 309.909001: <2> __arm64_sys_unshare+0x10/0x20
> 309.909004: <2> el0_svc_common+0xa0/0x158
> 309.909007: <2> el0_svc_handler+0x6c/0x88
> 309.909010: <2> el0_svc+0x8/0xc
> 309.909021: <6> neighbour: dev_put() ffffffe13c9df000 ip6_vti0
> refcnt valid addrconf_notify+0x42c/0xe58 -> ipv6_add_dev+0x400/0x588
> 309.909030: <6> IPv6: dev_put() ffffffe13c9df000 ip6_vti0 refcnt
> valid raw_notifier_call_chain+0x3c/0x68 -> addrconf_notify+0x42c/0xe58
> 309.918097: <6> neighbour: dev_put() ffffffe13c9df000 ip6_vti0
> refcnt valid raw_notifier_call_chain+0x3c/0x68 ->
> inetdev_event+0x290/0x528
> 309.918249: <6> dev_put() ffffffe13c9df000 ip6_vti0 refcnt valid
> register_netdevice+0x3f8/0x5b0 -> rollback_registered_many+0x488/0x658
> 309.918318: <6> dev_put() ffffffe13c9df000 ip6_vti0 refcnt valid
> net_rx_queue_update_kobjects+0x1ec/0x238 -> kobject_put+0x7c/0xc0
> 309.918405: <6> dev_put() ffffffe13c9df000 ip6_vti0 refcnt valid
> netdev_queue_update_kobjects+0x1dc/0x228 -> kobject_put+0x7c/0xc0
> 309.918759: <6> dev_put() ffffffe13c9df000 ip6_vti0 refcnt valid
> register_netdev+0x28/0x40 -> register_netdevice+0x3f8/0x5b0
> 309.918778: <6> free_netdev() ffffffe13c9df000 ip6_vti0 refcnt valid
> ops_init+0x88/0x110 -> vti6_init_net+0x1ac/0x1c0
> 309.980671: <6> dev_put() ffffffe13c9df000 ip6_vti0 refcnt null
> rcu_nocb_kthread+0x43c/0x468 -> in_dev_rcu_put+0x24/0x30
> 309.980838: <6> kernel BUG at include/linux/netdevice.h:3636!
Hello Eric
Could you please review this? The main concern here is that
dev_put() is getting called after free_netdev() causing a NULL
dereference.
309.918778: <6> free_netdev() ffffffe13c9df000 ip6_vti0 refcnt valid
ops_init+0x88/0x110 -> vti6_init_net+0x1ac/0x1c0
309.980671: <6> dev_put() ffffffe13c9df000 ip6_vti0 refcnt null
rcu_nocb_kthread+0x43c/0x468 -> in_dev_rcu_put+0x24/0x30
I am able to reproduce this consistently and open to testing
out patches.
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