Re: [PATCH net] e1000: add dummy allocator to fix race condition between mtu change and netpoll

[Jeff Kirsher <jeffrey.t.kirsher@intel.com>]

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On Wed, 2015-02-25 at 11:05 +0100, Sabrina Dubroca wrote:
> There is a race condition between e1000_change_mtu's cleanups and
> netpoll, when we change the MTU across jumbo size:
> 
> Changing MTU frees all the rx buffers:
>     e1000_change_mtu -> e1000_down -> e1000_clean_all_rx_rings ->
>         e1000_clean_rx_ring
> 
> Then, close to the end of e1000_change_mtu:
>     pr_info -> ... -> netpoll_poll_dev -> e1000_clean ->
>         e1000_clean_rx_irq -> e1000_alloc_rx_buffers ->
> e1000_alloc_frag
> 
> And when we come back to do the rest of the MTU change:
>     e1000_up -> e1000_configure -> e1000_configure_rx ->
>         e1000_alloc_jumbo_rx_buffers
> 
> alloc_jumbo finds the buffers already != NULL, since data (shared with
> page in e1000_rx_buffer->rxbuf) has been re-alloc'd, but it's garbage,
> or at least not what is expected when in jumbo state.
> 
> This results in an unusable adapter (packets don't get through), and a
> NULL pointer dereference on the next call to e1000_clean_rx_ring
> (other mtu change, link down, shutdown):
> 
> BUG: unable to handle kernel NULL pointer dereference at
> (null)
> IP: [<ffffffff81194d6e>] put_compound_page+0x7e/0x330
> 
>     [...]
> 
> Call Trace:
>  [<ffffffff81195445>] put_page+0x55/0x60
>  [<ffffffff815d9f44>] e1000_clean_rx_ring+0x134/0x200
>  [<ffffffff815da055>] e1000_clean_all_rx_rings+0x45/0x60
>  [<ffffffff815df5e0>] e1000_down+0x1c0/0x1d0
>  [<ffffffff811e2260>] ? deactivate_slab+0x7f0/0x840
>  [<ffffffff815e21bc>] e1000_change_mtu+0xdc/0x170
>  [<ffffffff81647050>] dev_set_mtu+0xa0/0x140
>  [<ffffffff81664218>] do_setlink+0x218/0xac0
>  [<ffffffff814459e9>] ? nla_parse+0xb9/0x120
>  [<ffffffff816652d0>] rtnl_newlink+0x6d0/0x890
>  [<ffffffff8104f000>] ? kvm_clock_read+0x20/0x40
>  [<ffffffff810a2068>] ? sched_clock_cpu+0xa8/0x100
>  [<ffffffff81663802>] rtnetlink_rcv_msg+0x92/0x260
> 
> By setting the allocator to a dummy version, netpoll can't mess up our
> rx buffers.  The allocator is set back to a sane value in
> e1000_configure_rx.
> 
> Fixes: edbbb3ca1077 ("e1000: implement jumbo receive with partial
> descriptors")
> Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
> ---
>  drivers/net/ethernet/intel/e1000/e1000_main.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)

Thanks Sabrina, I will add your patch to my queue.  It can be viewed at:
git://git.kernel.org/pub/scm/linux/kernel/git/jkirsher/queue.git
https://git.kernel.org/pub/scm/linux/kernel/git/jkirsher/queue.git
https://kernel.googlesource.com/pub/scm/linux/kernel/git/jkirsher/queue.git

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