panic on invalid ifp pointer in iflib drivers

[Keller, Jacob E]

> -----Original Message-----
> From: John Baldwin <jhb at FreeBSD.org>
> Sent: Thursday, October 17, 2019 9:31 AM
> To: Keller, Jacob E <jacob.e.keller at intel.com>; freebsd-net at freebsd.org
> Cc: shurd at llnw.com; Joyner, Eric <eric.joyner at intel.com>
> Subject: Re: panic on invalid ifp pointer in iflib drivers
> 
> Nominally, ifnet drivers should call ether_ifdetach first to remove public
> references to the ifnet and only call their stop routine after that has returned.
> This ensures any open if_ioctl invocations have completed, etc. before the
> stop routine is invoked.  Otherwise you are open to a race where the inteface
> can be upped via an ioctl after you have stopped the hardware.
> 
> Any other references to the ifnet via eventhandlers, etc. should also be
> deregistered before calling the stop routine.

Looks like iflib moved this much later when we refactored to add a shared function to deregister VLAN handlers...

> 
> After the hardware is stopped, interrupt handlers should be torn down and
> callouts
> and tasks drained to ensure there are no other references to the ifp outside of
> the thread running detach.
> 
> After that you can release device resources, destroy mutexes, free the ifp, etc.
> Note that drivers have to be prepared for ether_ifdetach to invoke if_ioctl (e.g.
> when detaching bpf), but of the drivers I've looked at this has generally been a
> non-issue.
> 
> It sounds like iflib should be doing the detach before calling iflib_stop.
> 

I tested a patch that moved ether_ifdetach above the call to iflib_stop.

This seems to have made the issue significantly harder to reproduce, but after multiple attach/detach cycles with IPv6 traffic: (INVARIANTS and WITNESS are enabled, as well as meguard protecting ifnet)

Unread portion of the kernel message buffer:
Kernel page fault with the following non-sleepable locks held:
exclusive sleep mutex ip6qlock (ip6qlock) r = 0 (0xfffffe00007aa848) locked @ /usr/src/sys/netinet6/frag6.c:849
shared rw vnet_rwlock (vnet_rwlock) r = 0 (0xffffffff820be700) locked @ /usr/src/sys/netinet6/frag6.c:845
stack backtrace:
#0 0xffffffff80bb6f83 at witness_debugger+0x73
#1 0xffffffff80bb7fa2 at witness_warn+0x442
#2 0xffffffff8108a0f3 at trap_pfault+0x53
#3 0xffffffff810896e4 at trap+0x2b4
#4 0xffffffff8106201c at calltrap+0x8
#5 0xffffffff80d8c07a at icmp6_error+0x4aa
#6 0xffffffff80d8b30e at frag6_freef+0x10e
#7 0xffffffff80d8b551 at frag6_slowtimo+0x111
#8 0xffffffff80bdcda4 at pfslowtimo+0x54
#9 0xffffffff80b65bdf at softclock_call_cc+0x13f
#10 0xffffffff80b65f9c at softclock+0x7c
#11 0xffffffff80b0f857 at ithread_loop+0x187
#12 0xffffffff80b0c4a4 at fork_exit+0x84
#13 0xffffffff8106305e at fork_trampoline+0xe

Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address   = 0xfffffe0000825dd8
fault code              = supervisor read data, page not present
instruction pointer     = 0x20:0xffffffff80d8c5b2
stack pointer           = 0x28:0xfffffe1fc28c6ff0
frame pointer           = 0x28:0xfffffe1fc28c7090
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 12 (swi4: clock (0))
trap number             = 12
panic: page fault
cpuid = 0
time = 1571354026
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe1fc28c6cb0
vpanic() at vpanic+0x19d/frame 0xfffffe1fc28c6d00
panic() at panic+0x43/frame 0xfffffe1fc28c6d60
trap_fatal() at trap_fatal+0x39c/frame 0xfffffe1fc28c6dc0
trap_pfault() at trap_pfault+0x62/frame 0xfffffe1fc28c6e10
trap() at trap+0x2b4/frame 0xfffffe1fc28c6f20
calltrap() at calltrap+0x8/frame 0xfffffe1fc28c6f20
--- trap 0xc, rip = 0xffffffff80d8c5b2, rsp = 0xfffffe1fc28c6ff0, rbp = 0xfffffe1fc28c7090 ---
icmp6_reflect() at icmp6_reflect+0x242/frame 0xfffffe1fc28c7090
icmp6_error() at icmp6_error+0x4aa/frame 0xfffffe1fc28c70e0
frag6_freef() at frag6_freef+0x10e/frame 0xfffffe1fc28c7130
frag6_slowtimo() at frag6_slowtimo+0x111/frame 0xfffffe1fc28c7180
pfslowtimo() at pfslowtimo+0x54/frame 0xfffffe1fc28c71b0
softclock_call_cc() at softclock_call_cc+0x13f/frame 0xfffffe1fc28c7260
softclock() at softclock+0x7c/frame 0xfffffe1fc28c7290
ithread_loop() at ithread_loop+0x187/frame 0xfffffe1fc28c72f0
fork_exit() at fork_exit+0x84/frame 0xfffffe1fc28c7330
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe1fc28c7330
--- trap 0, rip = 0, rsp = 0, rbp = 0 ---
KDB: enter: panic


Hmm.. now that I look at that more closely I think it's a separate issue.

> --
> John Baldwin