find stuck in state "clock"

[Simon 'corecode' Schubert]

Simon 'corecode' Schubert wrote:
Ok, I tried to play a bit Sherlock Holmes (on the live system).
Conclusion:

tcsh is terminating, calling exit(2).  The kernel closes all fdesc, 
including the controlling terminal ttyp5.  Trying to flush ttyp5, the 
vnode gets locked, but ttylclose/ttywflush blocks while the output queue 
is draining.

At the same time sshd, the process controlling ptsp5, does a chown of 
ttyp5.  For some reason it holds the namecache entry locked [*]. 
kern_chown tries to lock the vnode of ttyp5 and blocks on this attempt. 
 sshd can't read from ptsp5 and thus drain the output queue tcsh is 
waiting for.

Deadlock.

But I have no clue where do remove that deadlock.  Probably somewhere in 
the tty code and not in chown.  Any hints?

[*] The fact that the namecache entry is locked, doesn't lead to the 
deadlock, but it is the reason that dozens of find(1)s lock on /dev/ttyp5.

cheers
  simon
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