Subject: Strange hang in softintlock on SMP i386
To: None <,>
From: Thor Lancelot Simon <>
List: tech-kern
Date: 12/17/2005 01:56:57
One of the 4-cpu build machines hung in a very odd way tonight, after
being up and running happily for quite a while.

It won't respond on the network or on the console, though it *will* trap
to DDB.  What's interesting is what the first backtrace looks like any
time I enter DDB (if I exit DDB, it stays hung just like it was before,
though I can reenter DDB at will):

db{0}> trace
cpu_Debugger(842b5200,c,80100010,8f120030,10) at netbsd:cpu_Debugger+0x1
Xintr_ioapic_edge4() at netbsd:Xintr_ioapic_edge4+0x9c
--- interrupt ---
_kernel_lock(42,802c99c0,8f123f18,8010b848,802e6bd0) at

x86_softintlock(802e6bd0,802c99c0,7,8f123f38,801b4498) at
DDB lost frame for netbsd:Xsoftserial+0x18, trying 0x8f123f0c
Xsoftserial() at netbsd:Xsoftserial+0x18
--- interrupt ---
Bad frame pointer: 0x84784c00

Does this ring a bell for anyone?  The soft interrupt code and the
MP serial locking code make my head hurt.

 Thor Lancelot Simon	                            

"The inconsistency is startling, though admittedly, if consistency is to be
 abandoned or transcended, there is no problem."		- Noam Chomsky