Re: [E1000-devel] Possible bug in the i40evf driver

[Fujinaka, T. <tod...@in...>]

Thanks! We're having the developers look into this issue.

Todd Fujinaka
Software Application Engineer
Datacenter Engineering Group
Intel Corporation
tod...@in...
(503) 712-4565


-----Original Message-----
From: Codrut Grosu [mailto:co...@ix...] 
Sent: Tuesday, August 1, 2017 8:30 AM
To: e10...@li...
Subject: [E1000-devel] Possible bug in the i40evf driver

   Hi,

  We believe there might be a bug in the i40evf driver.

  We think that there is race issue between i40evf_reset_task and i40evf_down / i40evf_open.
The reason is that the functions napi_enable / napi_disable must be called in pairs in order not to loop indefinitely (or crash).

Consider the following:

ifconfig eth1 mtu 1000 & ifconfig eth1 up

What happens now is that the change of mtu schedules a reset. Suppose the reset task starts, and the first call to netif_running (after continue_reset) returns false. Before the thread reaches the second call to netif_running, i40evf_open starts in another thread. Then the second netif_running in reset will return true, and we will have 2 consecutive calls of napi_enable.

We could not reproduce this particular situation in practice (probably due to the short timing).
However, we did hang the driver using a call to ndo_close() followed quickly by "ethtool -G eth1 rx 4096". In this case netif_running will return true always (as we bypassed the call to dev_close), the reset will be scheduled before the interface finishes going down, and 2 calls to napi_disable will happen.

  Please let us know your opinion.

   Best wishes,
      Tudor, Codrut
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