"The "bad_page()" page allocator sanity check was reported recently (call chain as follows):

  bad_page+0x69/0x91
  free_hot_cold_page+0x81/0x144
  skb_release_data+0x5f/0x98
  __kfree_skb+0x11/0x1a
  tcp_ack+0x6a3/0x1868
  tcp_rcv_established+0x7a6/0x8b9
  tcp_v4_do_rcv+0x2a/0x2fa
  tcp_v4_rcv+0x9a2/0x9f6
  do_timer+0x2df/0x52c
  ip_local_deliver+0x19d/0x263
  ip_rcv+0x539/0x57c
  netif_receive_skb+0x470/0x49f
  :virtio_net:virtnet_poll+0x46b/0x5c5
  net_rx_action+0xac/0x1b3
  __do_softirq+0x89/0x133
  call_softirq+0x1c/0x28
  do_softirq+0x2c/0x7d
  do_IRQ+0xec/0xf5
  default_idle+0x0/0x50
  ret_from_intr+0x0/0xa
  default_idle+0x29/0x50
  cpu_idle+0x95/0xb8
  start_kernel+0x220/0x225
  _sinittext+0x22f/0x236

It occurs because an skb with a fraglist was freed from the tcp retransmit queue when it was acked, but a page on that fraglist had PG_Slab set (indicating it was allocated from the Slab allocator (which means the free path above can't safely free it via put_page.

We tracked this back to an nfsv4 setacl operation, in which the nfs code attempted to fill convert the passed in buffer to an array of pages in __nfs4_proc_set_acl, which gets used by the skb->frags list in xs_sendpages.  __nfs4_proc_set_acl just converts each page in the buffer to a page struct via virt_to_page, but the vfs allocates the buffer via kmalloc, meaning the PG_slab bit is set.  We can't create a buffer with kmalloc and free it later in the tcp ack path with put_page, so we need to either:

1) ensure that when we create the list of pages, no page struct has PG_Slab set

 or

2) not use a page list to send this data

Given that these buffers can be multiple pages and arbitrarily sized, I think (1) is the right way to go.  I've written the below patch to allocate a page from the buddy allocator directly and copy the data over to it.  This ensures that we have a put_page free-able page for every entry that winds up on an skb frag list, so it can be safely freed when the frame is acked.  We do a put page on each entry after the rpc_call_sync call so as to drop our own reference count to the page, leaving only the ref count taken by tcp_sendpages.  This way the data will be properly freed when the ack comes in

Successfully tested by myself to solve the above oops.

Note, as this is the result of a setacl operation that exceeded a page of data, I think this amounts to a local DOS triggerable by an uprivlidged user, so I'm CCing security on this as well."

Upstream commit:
http://git.kernel.org/linus/e9e3d724e2145f5039b423c290ce2b2c3d8f94bc

Introduced in 4b580ee3 v2.6.13-rc4