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

[Brandon Gooch]

On Thu, Aug 25, 2011 at 4:53 PM, Kostik Belousov <kostikbel at gmail.com> wrote:
> On Thu, Aug 25, 2011 at 03:16:09PM -0600, Charlie Martin 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.
> It is fine to ask there.
>
>>
>> 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.
> In 99% of the cases, it means that you forgot to dev_ref() some cdev.

So dev_ref increments the reference count for a cdev. Even though the
work "loop" seems to indicate that we will iterate over a list of
objects (one of which we may be missing a reference to via a missing
dev_ref()), I'm not seeing how this can cause a panic from inside
devfs_populate_loop().

Can you help me understand this?

-Brandon