softdep panic while low on memory during "make buildworld"
dillon at apollo.backplane.com
Fri Jan 25 11:52:14 PST 2008
:I got a "softdep_deallocate_dependencies: dangling deps" panic during
:"make buildworld" on a 64mb (virtual) machine. I'm running HEAD
:modified to allocate proc structs off an objcache instead of a zone.
:The panic is not reproducible with a stock HEAD build, so presumably
:the objcache has a bigger footprint but that's another story.
:softdep_deallocate_dependencies() is called from brelse():1088:
This has happened to me on a virtual machine too.
First, some background... softdeps holds onto buffers which have
dependancies, so if buf_deallocate() is EVER called on a softdep
bp, all softdep's callback does is panic because the situation is
not supposed to happen.
I haven't been able to track it down yet. The panic does not occur
very often at all and I was in the middle of some HAMMER debugging
when I got it and didn't want to switch modes, so to speak :-). It
has only happened to me once so far.
The VKERNEL's timing is very different from a normal kernel, and
most people run it with significantly less 'memory' then a real
kernel (I specify 64MB for the one I test HAMMER in, similar to
the 64MB vkernel you were using), and those differences tend to bring
out software bugs that are not normally apparent when running a
I am virtually certain that it is a bug in softdeps, probably related
to its low memory code which is almost never exercised on a normal kernel.
I don't know any more then that at the moment.
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