Subject: Re: kern/1774: Problems with identd/kvm_read
To: None <tech-kern@NetBSD.ORG>
From: Joao Carlos Mendes Luis <firstname.lastname@example.org>
Date: 11/20/1995 20:37:49
> > >Number: 1774
> > >Category: kern
> > >Synopsis: identd locking in kvm_read/lseek
> > Some times I note high CPU utilization, just to discover some
> > copies of identd running. System load (loadavg) equals 1 times
> > n copies, so I think it's in an infinite CPU loop.
> > When I call GDB and attach to one of these it's locked running
> > the getbuf function, running kvm_read in the shared lib area.
> > To be specific, it's locked inside the lseek() function.
> > Since none of identd.gebuf or lib/libkvm/kvm.c/kvm_read have
> > changed since on current, maybe this problem persists.
> > Seens to me a problem on /dev/kmem, in lseek, or even a race
> > condition with identd and a dying socket.
> hmm. interesting -- i have heard this from a few people on irc as well.
> if you are intestested in debugging this, could you compile identd
> with -g, and then next time it happens and you attach with gdb try to
> get a call trace. that will let me see where kvm_read is being called
> from (there are many ways to get to that function).
> thanks; hopefully we can squish this bug and i can commit it to the
> openbsd tree.
identd is heavily looping inside the getlist function. I don't know
the internal structure of PCBs, but surely something is wrong. All
my currently connection's PCB's start with 0xf8..., but pcbp->inp_next
holds a value of 0x400002a0 !
Probably a race conditions as I stated before, and a lost pointer
Oh, another problem. I was stepping around the loop with gdb and
suddenly my network connection stopped. I went to the console
just to see the KDB prompt saying: "stopped in syscall: push $0" or
something like that. All I have done was: "watch *pcbp" and lots of
I have ordered kdb to continue, and the system came back. The copy of
identd I was debugging simply got a SIGSEGV.
Joao Carlos Mendes Luis email@example.com
+55 21 290-4698 ( Job ) firstname.lastname@example.org
Network Manager UFRJ/COPPE/CISI
Universidade Federal do Rio de Janeiro