possible bug in the sbappendrecord_locked()? (Was: Re: core
dump with bluetooth device)
pluknet
pluknet at gmail.com
Sat Apr 18 14:41:47 UTC 2009
2009/4/17 Maksim Yevmenkin <maksim.yevmenkin at gmail.com>:
> On Thu, Apr 16, 2009 at 9:48 PM, pluknet <pluknet at gmail.com> wrote:
>> Sorry for top-posting.
>>
>> This is a fairly old bug.
>> See my investigation
>> http://lists.freebsd.org/pipermail/freebsd-net/2008-August/019345.html
>
> ahh, i see. thanks for the pointer. please read below.
>
>>>>>> <alexbestms at math.uni-muenster.de> wrote:
>>>>>>> hi there,
>>>>>>>
>>>>>>> i'm running r191076M. when i try to send files from my mobile phone to my
>>>>>>> computer via bt the core dumps. here's a backtrace:
>>>>>>>
>>>>>>> Unread portion of the kernel message buffer:
>>>>>>> sblastmbufchk: sb_mb 0xc8d54d00 sb_mbtail 0 last 0xc8d54d00
>>>>>>> packet tree:
>>>>>>> 0xc8d54d00
>>>>>>> panic: sblastmbufchk from /usr/src/sys/kern/uipc_sockbuf.c:797
>>>>>>> cpuid = 0
>>>>>>
>>>>>> are you, by change, have "options SOCKBUF_DEBUG" in your kernel?
>>>>>
>>>>> ok, there is something strange going on in the
>>>>> sbappendrecord_locked(). consider the following initial conditions:
>>>>>
>>>>> 1) sockbuf sb is empty, i.e. sb_mb == sb_mbtail == sb_lastrecord == NULL
>>>>>
>>>>> 2) sbappendrecord_locked() is given mbuf m0 with has exactly one mbuf,
>>>>> i.e. m0->m_next == NULL
>>>>>
>>>>> so
>>>>>
>>>>> void
>>>>> sbappendrecord_locked(struct sockbuf *sb, struct mbuf *m0)
>>>>> {
>>>>> struct mbuf *m;
>>>>>
>>>>> SOCKBUF_LOCK_ASSERT(sb);
>>>>>
>>>>> if (m0 == 0)
>>>>> return;
>>>>> m = sb->sb_mb;
>>>>>
>>>>> if (m)
>>>>> while (m->m_nextpkt)
>>>>> m = m->m_nextpkt;
>>>>>
>>>>> --> m is still NULL at this point
>>>>>
>>>>> /*
>>>>> * Put the first mbuf on the queue. Note this permits zero length
>>>>> * records.
>>>>> */
>>>>> sballoc(sb, m0);
>>>>> SBLASTRECORDCHK(sb);
>>>>>
>>>>> --> passed successfully, because sb_mb == sb_lastrecord == NULL (i.e.
>>>>> sockbuf is empty)
>>>>>
>>>>> SBLINKRECORD(sb, m0);
>>>>>
>>>>> --> at this point sb_mb == sb_lastrecord == m0, _but_ sb_mtail == NULL
>>>>>
>>>>> if (m)
>>>>> m->m_nextpkt = m0;
>>>>> else
>>>>> sb->sb_mb = m0;
>>>>>
>>>>> --> not sure about those lines above, didn't SBLINKRECORD(sb, m0) take
>>>>> care of it already?
>>>>> --> in any case, still, sb_mb == sb_lastrecord == m0 _and_ still
>>>>> sb_mtail == NULL
>>>>>
>>>>> m = m0->m_next;
>>>>> m0->m_next = 0;
>>>>>
>>>>> --> m is still NULL here
>>>>>
>>>>> if (m && (m0->m_flags & M_EOR)) {
>>>>> m0->m_flags &= ~M_EOR;
>>>>> m->m_flags |= M_EOR;
>>>>> }
>>>>>
>>>>> --> sbcompress() is called with m == NULL, which is triggers the panic
>>>>> (read below)
>>>>>
>>>>> sbcompress(sb, m, m0);
>>>>> }
>>>>>
>>>>> ===========
>>>>>
>>>>> void
>>>>> sbcompress(struct sockbuf *sb, struct mbuf *m, struct mbuf *n)
>>>>> {
>>>>> int eor = 0;
>>>>> struct mbuf *o;
>>>>>
>>>>> SOCKBUF_LOCK_ASSERT(sb);
>>>>>
>>>>> while (m) {
>>>>>
>>>>> --> lots of code that never gets executed because m == NULL
>>>>>
>>>>> }
>>>>> if (eor) {
>>>>> KASSERT(n != NULL, ("sbcompress: eor && n == NULL"));
>>>>> n->m_flags |= eor;
>>>>> }
>>>>>
>>>>> --> this where panic happens, because sb_mbtail is still NULL, but
>>>>> sockbuf now contains exactly one record
>>>>>
>>>>> SBLASTMBUFCHK(sb);
>>>>> }
>>>>>
>>>>> so, it looks like, sbcompress() should only be called when m != NULL.
>>>>> also, when m == NULL, m0 should be marked as EOR.
>>>>
>>>> actually, no, EOR should be set (or not set already).
>>>>
>>>>> comments anyone?
>
>
> ok, this is completely untested, so be warned :) would something like
> the following work? am i missing something?
I'm on vacations and will not able to test it until after 4/23. :(
>
>> svn diff
> Index: uipc_sockbuf.c
> ===================================================================
> --- uipc_sockbuf.c (revision 191012)
> +++ uipc_sockbuf.c (working copy)
> @@ -577,10 +577,6 @@
>
> if (m0 == 0)
> return;
> - m = sb->sb_mb;
> - if (m)
> - while (m->m_nextpkt)
> - m = m->m_nextpkt;
> /*
> * Put the first mbuf on the queue. Note this permits zero length
> * records.
> @@ -588,17 +584,17 @@
> sballoc(sb, m0);
> SBLASTRECORDCHK(sb);
> SBLINKRECORD(sb, m0);
> - if (m)
> - m->m_nextpkt = m0;
> - else
> - sb->sb_mb = m0;
> + sb->sb_mbtail = m0;
> m = m0->m_next;
> m0->m_next = 0;
> - if (m && (m0->m_flags & M_EOR)) {
> - m0->m_flags &= ~M_EOR;
> - m->m_flags |= M_EOR;
> + if (m != NULL) {
> + if (m0->m_flags & M_EOR) {
> + m0->m_flags &= ~M_EOR;
> + m->m_flags |= M_EOR;
> + }
> +
> + sbcompress(sb, m, m0);
> }
> - sbcompress(sb, m, m0);
> }
>
> /*
>
> ==
>
> thanks,
> max
>
--
wbr,
pluknet
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