svn commit: r265232 - head/sys/net

[Alan Somers]

On Fri, May 2, 2014 at 11:01 AM, Alexander V. Chernikov
<melifaro at freebsd.org> wrote:
> On 02.05.2014 20:24, Alan Somers wrote:
>>
>> Author: asomers
>> Date: Fri May  2 16:24:09 2014
>> New Revision: 265232
>> URL: http://svnweb.freebsd.org/changeset/base/265232
>>
>> Log:
>>    Fix a panic caused by doing "ifconfig -am" while a lagg is being
>> destroyed.
>>    The thread that is destroying the lagg has already set sc->sc_psc=NULL
>> when
>>    the "ifconfig -am" thread gets to lacp_req().  It tries to dereference
>>    sc->sc_psc and panics.  The solution is for lacp_req() to check the
>> value of
>>    sc->sc_psc.  If NULL, harmlessly return an lacp_opreq structure full of
>>    zeros.  Full details in GNATS.
>
> Sorry, it looks like I've missed -net@ discussion.

Thanks for the retroactive review; it's good too.

>
> While this patch minimizes panics, they still can occur.
> If one thread performs lagg_clone_destroy() -> lagg_lacp_detach() (1) ->
> lacp_detach(), executing
>
> struct lacp_softc *lsc = LACP_SOFTC(sc); (e.g. one line before sc_psc = NULL
> assignment)
>
> At the same moment, another thread (initiated by ifconfig) executes
>
>
> struct lacp_softc *lsc = LACP_SOFTC(sc);
>
> Then, thread #1 goes further to
>
> LACP_LOCK_DESTROY(lsc);
> free(lsc, M_DEVBUF);
>
> After that, thread #2 performs
>
> bzero(req, sizeof(struct lacp_opreq));
>
> passes lsc check for NULL and crashes on destroyed mutex.
>
>
> Briefly looking, we can remove WUNLOCK()  before lacp_detach() in
> lagg_lacp_detach() (I'm unsure about the reasons why do we need unlock
> here).
> lacp_req() is already protected by at least LAGG_RLOCK() so we should get
> consistent view of sc->sc_psc.

The WUNLOCK was added in r168561 without comment.  Removing it seems
like it would work.  It doesn't cause any new LORs or WITNESS
warnings.  And I can no longer reproduce the panic in lacp_req.
However, it doesn't fix another panic in lagg_port_ioctl line 825 (my
patch didn't either).  Do you have any good ideas what to do about
that?

#9  0xffffffff808cee81 in __mtx_lock_sleep (c=0xfffff800052bb648,
    tid=18446735277704396800, opts=<value optimized out>,
    file=<value optimized out>, line=<value optimized out>)
    at /usr/home/alans/freebsd/head/sys/kern/kern_mutex.c:430
#10 0xffffffff808ced02 in __mtx_lock_flags (c=<value optimized out>, opts=0,
    file=0xffffffff80f6dd8c
"/usr/home/alans/freebsd/head/sys/kern/kern_rmlock.c", line=407) at
/usr/home/alans/freebsd/head/sys/kern/kern_mutex.c:223
#11 0xffffffff808e0032 in _rm_rlock (rm=0xfffff800052bb608,
    tracker=0xfffffe0097751918, trylock=<value optimized out>)
    at /usr/home/alans/freebsd/head/sys/kern/kern_rmlock.c:407
#12 0xffffffff808e0812 in _rm_rlock_debug (rm=0xfffff800052bb608,
    tracker=0xfffffe0097751918, trylock=0,
    file=0xffffffff81c1dd13
"/usr/home/alans/freebsd/head/sys/modules/if_lagg/../../net/if_lagg.c",
line=825)
    at /usr/home/alans/freebsd/head/sys/kern/kern_rmlock.c:659
#13 0xffffffff81c19f62 in lagg_port_ioctl (ifp=0xfffff8000590d800,
    cmd=<value optimized out>, data=0xfffff80005582c00 "tap0")
    at /usr/home/alans/freebsd/head/sys/modules/if_lagg/../../net/if_lagg.c:825
#14 0xffffffff809ae407 in ifioctl (so=<value optimized out>, cmd=3225971084,
    data=0xfffff80005582c00 "tap0", td=<value optimized out>)
    at /usr/home/alans/freebsd/head/sys/net/if.c:2643
#15 0xffffffff8093b9fb in kern_ioctl (td=<value optimized out>,
    fd=<value optimized out>, com=<value optimized out>) at file.h:323
#16 0xffffffff8093b77c in sys_ioctl (td=0xfffff800053cc000,
    uap=0xfffffe0097751b80)
    at /usr/home/alans/freebsd/head/sys/kern/sys_generic.c:702