Date: Fri, 10 Jun 2005 14:19:37 -0400 From: Stephan Uphoff <ups@tree.com> To: Kris Kennaway <kris@obsecurity.org> Cc: "current@freebsd.org" <current@freebsd.org> Subject: Re: mutex still spinning while in DDB on UP machine Message-ID: <1118427576.27369.54212.camel@palm> In-Reply-To: <20050609183835.GA9451@xor.obsecurity.org> References: <20050609183835.GA9451@xor.obsecurity.org>
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On Thu, 2005-06-09 at 14:38, Kris Kennaway wrote:
> I've seen the following a couple of times recently on UP machines
> running up-to-date current (the panic may not be important, I'm
> referring to the behaviour of DDB):
>
> Fatal trap 12: page fault while in kernel mode
> fault virtual address = 0x0
> fault code = supervisor write, page not present
> instruction pointer = 0x20:0xc054cc77
> stack pointer = 0x28:0xd4222c9c
> frame pointer = 0x28:0xd4222cb4
> 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 = 37 (vnlru)
> [thread pid 37 tid 100035 ]
> Stopped at vnlru_free+0x87: movl %eax,0(%edx)
> db> stray irq7
> stray irq7
> stray irq7
> stray irq7
> too many stray irq 7's: not logging anymore
>
> At this point, the keyboard only works sporadically (i.e. I have to
> press keys multiple times for DDB to receive the input).
>
> show ktr shows a buffer full of:
>
> 530: UNLOCK (spin mutex) icu r = 0 at ../../../i386/isa/atpic.c:267
> 529: LOCK (spin mutex) icu r = 0 at ../../../i386/isa/atpic.c:265
> [ ..SNIP....]
> and repeated show ktr indicates that it is still logging events
> (i.e. the head of the buffer is now in a different place). This
> suggests that the mutex is still spinning even though the system is in
> DDB.
>
> Kris
Kris,
the following patch should help as it disables interrupts before
entering the debugger. (amd64 probably has the same problems and I will
take a look later today )
Could you give it a spin? I would like to check it in ASAP.
Stephan
Index: trap.c
===================================================================
RCS file: /cvsroot/src/sys/i386/i386/trap.c,v
retrieving revision 1.274
diff -u -r1.274 trap.c
--- trap.c 30 May 2005 06:29:28 -0000 1.274
+++ trap.c 10 Jun 2005 18:11:01 -0000
@@ -823,8 +823,15 @@
}
#ifdef KDB
- if ((debugger_on_panic || kdb_active) && kdb_trap(type, 0,
frame))
- return;
+ if (debugger_on_panic || kdb_active) {
+ register_t eflags;
+ eflags = intr_disable();
+ if (kdb_trap(type, 0, frame)) {
+ intr_restore(eflags);
+ return;
+ }
+ intr_restore(eflags);
+ }
#endif
printf("trap number = %d\n", type);
if (type <= MAX_TRAP_MSG)
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