Where to ask about a 7.2 bug, and debugging sys/queue.h errors

[Kip Macy]

On Thu, Aug 25, 2011 at 11:16 PM, Charlie Martin <crmartin at sgi.com> wrote:
> We're having a crash in some internal code running on FreeBSD 7.2
> (specifically  7.2-PRERELEASE FreeBSD 7.2-PRERELEASE and yeah, I know it's
> quite a bit behind) in which after 18-30 hours of running load tests, the
> code panics with:
>
> panic: Bad link elm 0xffffff0044c09600 next->prev != elm
> cpuid = 0
> KDB: stack backtrace:
> db_trace_self_wrapper() at 0xffffffff8019119a = db_trace_self_wrapper+0x2a
> panic() at 0xffffffff80307c72 = panic+0x182
> devfs_populate_loop() at 0xffffffff802a43a8 = devfs_populate_loop+0x548
>
>
> First question: where's the most appropriate place to ask about this kind of
> bug on a back version.

Probably -stable. I don't know how many developers are still running
7. Most are on 8 at this point.

> Second: does this remind anyone of any bugs?  Googling came up with a few
> somewhat similar things but hasn't provided much insight so far.

This panic is very common when list updates aren't adequately serialized.

> Third: I tried compiling with the sys/queue.h QUEUE_MACRO_DEBUG defined in
> order to get more useful information from the panic.  The kernel build fails
> in pmap.c when this macro is defined, giving an error saying the CTASSERT
> macro is resolving to a negative array size.  Is there any particular secret
> to using this macro (like, no one goes there any more?)

This is because you are running amd64 and the the pv_entry constants
were defined assuming the default (smaller) list entry structure. I
once fixed this in a local tree, but I think I was so dismayed at the
"obviousness" of the bug I was tracking down that I neglected to
commit the pmap update. It shouldn't be too hard to calculate the
correct constants.

Cheers