Re: Recent changes to pseudofs causing panics -- leaking a vnode lock?

On Fri, Jan 9, 2009 at 2:49 PM, Joe Marcus Clarke <marcus_at_freebsd.org> wrote:
> On Thu, 2009-01-08 at 18:48 -0600, Richard Todd wrote:
>> I've noticed that ever since updating to a kernel after the recent changes
>> to the pseudofs code late last month, that I've occasionally gotten the
>> following sort of panic:
>>
>> System call readlink returning with the following locks held:
>> exclusive lockmgr pseudofs (pseudofs) r = 0 (0xffffff00ba581cc8) locked _at_ /usr/src/sys/fs/pseudofs/pseudofs_vncache.c:193
>> panic: witness_warn
>>
>> The line in question is the one I marked by an arrow in this chunk of the
>> pfs_vncache_alloc code:
>>         if ((pn->pn_flags & PFS_PROCDEP) != 0)
>>                 (*vpp)->v_vflag |= VV_PROCDEP;
>>         pvd->pvd_vnode = *vpp;
>>         VN_LOCK_AREC(*vpp);
>>         vn_lock(*vpp, LK_EXCLUSIVE | LK_RETRY); <==== this lock here
>>         error = insmntque(*vpp, mp);
>>
>> So somehow, a vnode is getting locked here and not getting unlocked.
>> I suspect the code in the retry2: loop later, simply because that's
>> the code that got added in the late December commits, but I'm not
>> clear on how exactly.  I've tried littering the code with extra
>> printfs to try to clarify what's going on, but alas, I'm still not
>> really sure what's going on.  I do have a good coredump that I can get
>> info out of, if someone can suggest to me what would be useful things
>> to dump.  Anyway, here's the patch for the debugging printfs I added,
>> and the console messages produced by those printfs from the most
>> recent coredump/panic.  The console msgs do seem to indicate some sort
>> of race condition going on, though, as they seem to show two or more processes
>> simultaneously hitting the pseudofs code and hitting my debugging print
>> statements (alas, making the console log rather a confused mess.)
>
> I believe I have fixed this in HEAD.  Kib gave his review and approval,
> and the fix really should prevent this hang.  Please report back if you
> still see the problem.
>
> Joe

Joe,
    When did you do this commit / what's the SVN revision #?
Thanks!
-Garrett