Re: IB/ipoib: fix dangling pointer reference to ipoib_neigh and ipoib_path -when will it go upstream?

[Pradeep Satyanarayana <pradeeps-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>]

Pradeep Satyanarayana wrote:
> Pradeep Satyanarayana wrote:
>> Roland Dreier wrote:
>>>  > I guess I came to a premature conclusion. One set of tests ran fine and I made that
>>>  > conclusion. Another set of tests caused the following crash:
>>>
>>> I don't really know how to interpret this.  Is this crash new, or is it
>>> the same crash you were hoping this patch fixed?
>> This is a new crash.
> 
> I see other manifestations resulting in different crashes :
> 
> :mon> t
> [c00000074603ba20] d0000000193527ac .ipoib_neigh_flush+0x6c/0x350 [ib_ipoib]
> [c00000074603bb10] d000000019356dac .ipoib_mcast_free+0x74/0x2a0 [ib_ipoib]
> [c00000074603bbe0] d000000019358558 .ipoib_mcast_restart_task+0x3d0/0x560 [ib_ipoib]
> [c00000074603bd40] c0000000000c6fe4 .run_workqueue+0xf4/0x1e0
> [c00000074603be00] c0000000000c7190 .worker_thread+0xc0/0x180
> [c00000074603bed0] c0000000000ccf4c .kthread+0xb4/0xc0
> [c00000074603bf90] c0000000000309fc .kernel_thread+0x54/0x70
> 9:mon> e
> cpu 0x9: Vector: 300 (Data Access) at [c00000074603b720]
>     pc: c0000000005ac390: ._spin_lock+0x20/0xc8
>     lr: d0000000193527ac: .ipoib_neigh_flush+0x6c/0x350 [ib_ipoib]
>     sp: c00000074603b9a0
>    msr: 8000000000009032
>    dar: 3a0
>  dsisr: 40000000
>   current = 0xc000000756ce8b00
>   paca    = 0xc000000000f63800
>     pid   = 18095, comm = ipoib
> 9:mon>

Recreating the crash has been tricky. I have tried several several hundred times today
to unload and reload IPoIB while there is traffic and no crashes happened. I took
a closer look at the IPoIB CM code and I see a few things that look suspicious.

In the ipoib_cm_send() path no priv->lock is held, whereas the priv->lock is held before 
calling ipoib_cm_destroy_tx(). This is true with and without Ralph's patch (fix dangling pointer).
Is this a potential race?

In Roland's git tree I do see a test_and_clear_bit(IPOIB_FLAG_INITIALIZED, &tx->flags) in 
ipoib_cm_destroy_tx() which seems to be missing in Ralph's patch. In Ralph's patch) there is a 
clear_bit(IPOIB_FLAG_OPER_UP, &tx->flags) called before calling ipoib_cm_destroy_tx() only in 
select cases. Was that intended?

Thanks
Pradeep

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