locked vnode / nfs... requires kill -9 in ddb

[John E Hein]

Kostik Belousov wrote at 06:57 +0300 on Oct 21, 2006:
 > On Sat, Oct 21, 2006 at 08:25:00AM +0800, David Xu wrote:
 > > On Thursday 19 October 2006 18:04, Kostik Belousov wrote:
 > > 
 > > >
 > > > The nfs_reply is sleeping with the PCATCH set. The question is why SIGTSTP
 > > > does not cause msleep to return with EINTR.
 > > 
 > > I have not been tracking the thread. but if the thread is sleeping with
 > > PCATCH, the SIGTSTP should cause the process to stop unless the signal
 > > is masked by sigprocmask or the signal has an action handler been set, 
 > > this is  a correct behavior.
 > > 
 > David,
 > as I understand the report, the following happens. The nfs mount point with
 > intr option issued the request and waits for the reply. Some vnode locks are
 > held while waiting. Code needs to catch the signals to abort the operation
 > on user request. It uses msleep with PCATCH. The thread in question has
 > td_locks > 0.
 > 
 > The SIGTSTP is delivered, and thread is stopped, while holding vnode lock.
 > How this situation shall be handled ? Namely, how to sleep while having the
 > ability to safely clean up on attempt of stopping ? Masking SIGTSTP is not
 > the option, due to SIGSTOP having the same results and not being blockable.
 > 
 > [Would it be right to stop the threads only on returning from kernel to user
 > mode ?]

David, here's the original report.
http://lists.freebsd.org/pipermail/freebsd-stable/2006-October/029755.html

Indeed, as Kostik surmised, the mount point is mounted intr.

I did not notice this problem while running with releng_6 from late
June for 3 months.  Could it be this problem was introduced between
then and now?

This also just happened today on a system I just updated from 5.3
to 5.5-p8.