Re: 3.17-rc1 oops during network interface configuration

Chuck Lever
2014-09-09T19:30:51Z

On Aug 20, 2014, at 6:31 AM, Or Gerlitz <ogerlitz@mellanox.com> wrote:

> On 18/08/2014 15:18, Bart Van Assche wrote:
>> Has anyone else already tried to boot kernel 3.17-rc1 on an IB system ? The
>> following call trace is triggered during boot on a system on which kernel
>> 3.16 runs fine:
>
> Yep, I see it on my systems too.
>
> I narrowed this down a bit to happen only when the port link type (these nodes have ConnectX) is IB and IPoIB gets to load.
>
> I reverted (below) all the IPoIB changes since 3.16 (except for the trivial commit c835a67) and the crash still exists.
>
> I guess this needs to go through systematic bisection.

This crash happens when booting v3.17-rcN on any of my IB-enabled
systems. I have both ConnectX-2 and mthca systems, all are affected.

I bisected this to:

commit e0f31d8498676fda36289603a054d0d490aa2679
Author: Govindarajulu Varadarajan <_govind@gmx.com>
AuthorDate: Mon Jun 23 16:07:58 2014 +0530
Commit: David S. Miller <davem@davemloft.net>
CommitDate: Mon Jun 23 14:32:19 2014 -0700

flow_keys: Record IP layer protocol in skb_flow_dissect()

skb_flow_dissect() dissects only transport header type in ip_proto. It dose not
give any information about IPv4 or IPv6.
This patch adds new member, n_proto, to struct flow_keys. Which records the
IP layer type. i.e IPv4 or IPv6.
This can be used in netdev->ndo_rx_flow_steer driver function to dissect flow.
Adding new member to flow_keys increases the struct size by around 4 bytes.
This causes BUILD_BUG_ON(sizeof(qcb->data) < sz); to fail in
qdisc_cb_private_validate()
So increase data size by 4

Signed-off-by: Govindarajulu Varadarajan <_govind@gmx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This commit includes a hunk that increases the size of struct qdisc_skb_cb
by at least 4 bytes:

> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
> index 624f985..a3cfb8e 100644
> --- a/include/net/sch_generic.h
> +++ b/include/net/sch_generic.h
> @@ -231,7 +231,7 @@ struct qdisc_skb_cb {
> unsigned int pkt_len;
> u16 slave_dev_queue_mapping;
> u16 _pad;
> - unsigned char data[20];
> + unsigned char data[24];
> };
>
> static inline void qdisc_cb_private_validate(const struct sk_buff *skb, int sz)

IPoIB defines the following structure in drivers/infiniband/ulp/ipoib/ipoib.h:

> struct ipoib_cb {
> struct qdisc_skb_cb qdisc_cb;
> u8 hwaddr[INFINIBAND_ALEN];
> };

IPoIB keeps this in the sk_buff:cb field, which is exactly 48 bytes.
After commit e0f31d84, the size of struct ipoib_cb on x86_64 becomes
52 bytes.

Thus IPoIB overruns sk_buff:cb, and trashes the sk_buff::_skb_refdst
field, which contains a pointer. By the time we get into
__dev_queue_xmit() and try to use the result of skb_dst(), that pointer
is garbage, and we oops.

Obviously, cb[] could be increased to 56 bytes to accommodate struct
ipoib_cb. I tried this, and it is effective in preventing the oops on
one of my systems.

But I suspect there is an historical reason I’m not aware of that it
has remained 48 bytes for years.

> Or.
>
>> net.git]# git log --oneline --no-merges v3.16.. drivers/infiniband/ulp/ipoib/
>> 8a118a4 Revert "IB/ipoib: Use P_Key change event instead of P_Key polling mechanism"
>> 90e6f39 Revert "IB/ipoib: Avoid flushing the workqueue from worker context"
>> 030ade7 Revert "IB/ipoib: Avoid multicast join attempts with invalid P_key"
>> 97ba2ff Revert "IPoIB: Remove unnecessary test for NULL before debugfs_remove()"
>> e42fa20 IPoIB: Remove unnecessary test for NULL before debugfs_remove()
>> dd57c93 IB/ipoib: Avoid multicast join attempts with invalid P_key
>> 4eae374 IB/ipoib: Avoid flushing the workqueue from worker context
>> db84f88 IB/ipoib: Use P_Key change event instead of P_Key polling mechanism
>> c835a67 net: set name_assign_type in alloc_netdev()
>
>
>> BUG: unable to handle kernel paging request at ffff88090000007e
>> IP: __dev_queue_xmit+0x519
>> Call Trace:
>> ? __dev_queue_xmit+0x49
>> dev_queue_xmit+0x10
>> neigh_connected_output
>> ? ip_finish_output
>> ip_finish_output
>> ? ip_finish_output
>> ? netif_rx_ni
>> ip_mc_output
>> ip_local_out_sk
>> ip_send_skb
>> udp_send_skb
>> udp_sendmsg
>> ? ip_reply_glue_bits
>> ? __lock_is_held
>> inet_sendmsg
>> ? inet_sendmsg
>> sock_sendmsg
>> ? might_fault
>> ? might_fault
>> ? move_addr_to_kernel.part.38
>> SYSC_sendto
>> ? sysret_check
>> ? trace_hardirqs_on_caller
>> ? trace_hardirqs_on_thunk
>> SyS_sendto
>> system_call_fastpath
>>
>> Kernel panic - not syncing: Fatal exception in interrupt
>> Kernel Offset: 0x0 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffff9fffffff)
>> drm_kms_helper: panic occurred, switching back to text console
>>
>> A screenshot of this kernel oops can be found here:
>> https://drive.google.com/file/d/0B1YQOreL3_FxVDB5UTNwekF6LVU/
>>
>> gdb translates the crash address into the following (not sure this makes sense
>> since offset 0x519 is past the end of __dev_queue_xmit()):
>>
>> (gdb) list *(__dev_queue_xmit+0x519)
>> 0xffffffff8136bc89 is in netdev_adjacent_rename_links (net/core/dev.c:5167).
>> 5162 void netdev_adjacent_rename_links(struct net_device *dev, char *oldname)
>> 5163 {
>> 5164 struct netdev_adjacent *iter;
>> 5165
>> 5166 list_for_each_entry(iter, &dev->adj_list.upper, list) {
>> 5167 netdev_adjacent_sysfs_del(iter->dev, oldname,
>> 5168 &iter->dev->adj_list.lower);
>> 5169 netdev_adjacent_sysfs_add(iter->dev, dev,
>> 5170 &iter->dev->adj_list.lower);
>> 5171 }
>>
>> And the address __dev_queue_xmit+0x49 is translated by gdb into:
>>
>> (gdb) list *(__dev_queue_xmit+0x49)
>> 0xffffffff8136b7b9 is in __dev_queue_xmit (./arch/x86/include/asm/preempt.h:75).
>> 70 * The various preempt_count add/sub methods
>> 71 */
>> 72
>> 73 static __always_inline void __preempt_count_add(int val)
>> 74 {
>> 75 raw_cpu_add_4(__preempt_count, val);
>> 76 }
>> 77
>> 78 static __always_inline void __preempt_count_sub(int val)
>> 79 {
>
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--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com