Segfault seen in netmap_compat app on Power8

Segfault seen in netmap_compat app on Power8

[Rahul Lakkireddy]

Hi,

For netmap_compat bridge application on Power8, in netmap_regif
function, the assignment to nmif->ring_ofs[i] is not getting reflected
immediately.

As a result, the subsequent call to netmap_ring_setup ends up writing
data at wrong offset. This causes segfault in the app.

If we print the nmif->ring_ofs[i] after assignment, then, we see the
correct offset and application starts fine.

So, probably, some kind of barrier or mechanism to flush write is
required on Power8?

BTW, this was tried with ToT dpdk git tree on RHEL 7.3 having below
gcc version:

gcc version 4.8.5 20150623 (Red Hat 4.8.5-11) (GCC)

Thanks,
Rahul

Re: Segfault seen in netmap_compat app on Power8

[gowrishankar muthukrishnan]

With gcc 6.3.0, I find this app functioning w/o crash.

Did disabling gcc optimization help ? (set EXTRA_CFLAGS='-O0' before 
compile).

Regards,
Gowrishankar
On Thursday 06 April 2017 02:34 PM, Rahul Lakkireddy wrote:
> Hi,
>
> For netmap_compat bridge application on Power8, in netmap_regif
> function, the assignment to nmif->ring_ofs[i] is not getting reflected
> immediately.
>
> As a result, the subsequent call to netmap_ring_setup ends up writing
> data at wrong offset. This causes segfault in the app.
>
> If we print the nmif->ring_ofs[i] after assignment, then, we see the
> correct offset and application starts fine.
>
> So, probably, some kind of barrier or mechanism to flush write is
> required on Power8?
>
> BTW, this was tried with ToT dpdk git tree on RHEL 7.3 having below
> gcc version:
>
> gcc version 4.8.5 20150623 (Red Hat 4.8.5-11) (GCC)
>
> Thanks,
> Rahul
>
>

Re: Segfault seen in netmap_compat app on Power8

[Rahul Lakkireddy]

On Thursday, April 04/06/17, 2017 at 15:06:03 +0530, gowrishankar muthukrishnan wrote:
>    With gcc 6.3.0, I find this app functioning w/o crash.
> 
>    Did disabling gcc optimization help ? (set EXTRA_CFLAGS='-O0' before
>    compile).
> 

Yes, with optimization disabled, the app is not hitting the segfault.

Thanks,
Rahul

>    Regards,
>    Gowrishankar
>    On Thursday 06 April 2017 02:34 PM, Rahul Lakkireddy wrote:
>    > Hi,
>    >
>    > For netmap_compat bridge application on Power8, in netmap_regif
>    > function, the assignment to nmif->ring_ofs[i] is not getting reflected
>    > immediately.
>    >
>    > As a result, the subsequent call to netmap_ring_setup ends up writing
>    > data at wrong offset. This causes segfault in the app.
>    >
>    > If we print the nmif->ring_ofs[i] after assignment, then, we see the
>    > correct offset and application starts fine.
>    >
>    > So, probably, some kind of barrier or mechanism to flush write is
>    > required on Power8?
>    >
>    > BTW, this was tried with ToT dpdk git tree on RHEL 7.3 having below
>    > gcc version:
>    >
>    > gcc version 4.8.5 20150623 (Red Hat 4.8.5-11) (GCC)
>    >
>    > Thanks,
>    > Rahul
>    >
>    >