cvs commit: src/sys/net if_vlan.c

[Yar Tikhiy]

On Thu, Jun 29, 2006 at 04:36:30PM +0200, Andre Oppermann wrote:
> Yar Tikhiy wrote:
> >On Thu, Jun 29, 2006 at 01:24:56PM +0400, Maxim Konovalov wrote:
> >>On Thu, 29 Jun 2006, 07:52-0000, Yar Tikhiy wrote:
> >>
> >>>yar         2006-06-29 07:52:30 UTC
> >>>
> >>>  FreeBSD src repository
> >>>
> >>>  Modified files:
> >>>    sys/net              if_vlan.c
> >>>  Log:
> >>>  Detach the interface first, do vlan_unconfig() then.
> >>>  Previously, another thread could get a pointer to the
> >>>  interface by scanning the system-wide list and sleep
> >>>  on the global vlan mutex held by vlan_unconfig().
> >>>  The interface was gone by the time the other thread
> >>>  woke up.
> >>>
> >>>  In order to be able to call vlan_unconfig() on a detached
> >>>  interface, remove the purely cosmetic bzero'ing of IF_LLADDR
> >>>  from the function because a detached interface has no addresses.
> >>>
> >>>  Noticed by:     a stress-testing script by maxim
> >>>  Reviewed by:    glebius
> >>Still no cookie :-)
> >>
> >>db> bt
> >>Tracing pid 75800 tid 100098 td 0xc2b0e960
> >>in_control(c2a1c67c,c02069f6,c40eece0,c2e66000,c2b0e960) at 
> >>in_control+0x114
> >>ifioctl(c2a1c67c,c02069f6,c40eece0,c2b0e960,0,...) at ifioctl+0xee
> >>soo_ioctl(c27cb4c8,c02069f6,c40eece0,c2c04980,c2b0e960) at soo_ioctl+0x2db
> >>ioctl(c2b0e960,d56a4d04) at ioctl+0x370
> >>syscall(3b,3b,3b,bfbfe2c4,0,...) at syscall+0x27e
> >>Xint0x80_syscall() at Xint0x80_syscall+0x1f
> >>--- syscall (54, FreeBSD ELF32, ioctl), eip = 0x2817cb43, esp =
> >>0xbfbfe28c, ebp = 0xbfbfe2d8 ---
> >>
> >>Let me know if you need more info.
> >
> >I stress tested gif(4) in the same manner for kicks and got a very
> >similar panic in in_control().  I suppose that my change eliminated
> >a concurrency problem in vlan(4) and we began to feel the lack of
> >refcounting at ifnet level.  Indeed, a thread can keep a pointer
> >to an ifnet beyond its lifetime and panic the system on access to
> >the dead ifnet.
> 
> For the time being we should simply mark ifnet's dead but keep them
> around. Refcounting is most likely too expensive, especially on larger
> SMP systems. All users of ifnets then have to be teached to obey the
> dead flag.

AFAIK we refcount vnodes, which are an object used rather heavily.
Do you think refcounting ifnets would be worse than that?

-- 
Yar