Re: Page fault in IFNET_WLOCK_ASSERT [if.c and pccbb.c]

On Sat, Oct 17, 2009 at 11:42 PM, Julian Elischer <julian_at_elischer.org> wrote:
> Harsha wrote:
>> <rwatson_at_freebsd.org> wrote:
>>>
>>> Looks like a NULL pointer dereference, so perhaps a more traditional bug
>>> --
>>> could you convert ifindex_alloc_locked+0x71 to a line of code? You can do
>>> this using kgdb on the kernel symbols file, perhaps "l
>>> *ifindex_alloc_locked+0x71".
>>
>> It is the for loop in ifindex_alloc_locked() function-
>>  for (idx = 1; idx <= V_if_index; idx++)
>>
>> idx is a local variable, so I figured it is V_if_index is what is
>> causing the page fault. It does look like a NULL pointer reference - I
>> see that V_if_index comes from that  vnet instance's value and uses
>> the macro VNET_VNET_PTR() down the chain. Since the call chain is
>> coming from a new thread cbb_event_thread, I believe that this
>> thread's vnet context needs to be set using CURVNET_SET().
>
> but only if you have options VIMAGE defined. if not then CURVNET_SET()
> is a NOP
I do have the VIMAGE options turned on.

Can someone tell me what is the right way to add the vnet context to
cbb_event_thread?

I tried adding context in two locations-

1. In cbb_insert() as-
CURVNET_SET(TD_TO_VNET(curthread));

2. In if_alloc() as-
CURVNET_SET(TD_TO_VNET(curthread));

or as

ifp = malloc(sizeof(struct ifnet), M_IFNET, M_WAITOK|M_ZERO);
#ifdef VIMAGE
      ifp->if_vnet = curvnet;
      if (ifp->if_home_vnet == NULL)
          ifp->if_home_vnet = curvnet;
      CURVNET_SET(ifp->if_vnet);
#endif

But in all the cases I get a warning/error about unused variable
'saved_vnet' like this-

cc1: warnings being treated as errors
/usr/src/sys/net/if.c: In function 'if_alloc':
/usr/src/sys/net/if.c:418: warning: unused variable 'saved_vnet'

The backtrace is in the link I posted earlier.

Thanks,
Harsha