Date: Fri, 14 Aug 1998 02:45:46 +0200 (CEST) From: Stefan Bethke <stb@hanse.de> To: freebsd-stable@FreeBSD.ORG Cc: freebsd-current@FreeBSD.ORG Subject: Re: Huge Bug in FreeBSD not fixed? Message-ID: <Pine.BSF.3.96.980814023617.9883A-300000@transit.hanse.de> In-Reply-To: <1682190.3111854089@d254.promo.de>
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--0-1089576808-903055546=:9883
Content-Type: TEXT/PLAIN; charset=US-ASCII
[ please followup technical discussions to -current. ]
On Tue, 11 Aug 1998, Stefan Bethke wrote:
> On Die, 11. Aug 1998 13:33 Uhr +0200 Thomas Gellekum
> <tg@ihf.rwth-aachen.de> wrote:
>
> > I have run this program five times and it finished once. The other
> > four occasions I got
> >
> > Fatal trap 12: page fault while in kernel mode
> > fault virtual address = 0x18
> > fault code = supervisor write, page ot present
> > instruction pointer = 0x8:0xf0126d21
> > stack pointer = 0x10:0xefbffe50
> > frame pointer = 0x10:0xefbffe74
> > code segment = base 0x0, limit 0xfffff, type 0x1b
> > = DPL 0, pres 1, def32 1, gran 1
> > processor eflags = interrupt enabled, resume, IOPL = 0
> > current process = 395 (crashbsd)
> > interrupt mask =
> > kernel: type 12 trap, code=0
> > Stopped at _sosend+0x391: movl $0, 0x18(%ebx)
> >
> > After saving the core dump and recompiling a few object files with -g:
>
> > #9 0xf01c0a37 in trap (frame={tf_es = -2147483632, tf_ds = -272695280,
> > tf_edi = -272630136, tf_esi = -2147483648, tf_ebp = -272630156,
> > tf_isp = -272630212, tf_ebx = 0, tf_edx = 2147483647,
> > tf_ecx = -1073277766, tf_eax = 0, tf_trapno = 12, tf_err = 2,
> > tf_eip = -267227871, tf_cs = 8, tf_eflags = 66198, tf_esp = 0,
> > tf_ss = 1}) at ../../i386/i386/trap.c:324
> > #10 0xf0126d21 in sosend (so=0xf0937f00, addr=0x0, uio=0xefbffeb0,
> > top=0x0, control=0xf06fff00, flags=0) at ../../kern/uipc_socket.c:432
>
> Looking at kern/uipc_socket.c:sosend(), one can easily spot the problem
> Because sosend() expects a MGET(m, M_WAIT, MT_DATA) to always succeed, it
> pagefaults while trying to manipulate the non-allocated mbuf
> (m->m_pkthdr.len at 0+0x18).
> The solution would be either to make MGET() and MGETHRD() to always succeed
> (or sleep indefinitly), or check the result of any of those calls (as many
> callers already do).
> This in both -stable and -current.
I've made a simple patch to uipc_mbuf.c that makes sure M_GET() and
M_GETHDR() always succeed when called with M_WAIT.
The patch (attached) is against -current about 48 hrs ago.
I've done a little testing (slightly modified version of the test program,
also attached). It *seems* to work. I'd really appreciate comments from
those more knowledgable...
Cheers,
Stefan
--
Stefan Bethke
Muehlendamm 12 Phone: +49-40-256848, +49-177-3504009
D-22087 Hamburg <stefan.bethke@hanse.de>
Hamburg, Germany <stb@freebsd.org>
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