Processes stuck in D state

[Olaf Kirch <okir@suse.de>]

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Hi,

I spent much of today investigating a weird NFS problem on 2.6.3.

After one of our servers went away and came back, several processes on
a ppc machine were left in D state. They did not get woken up during
the whole day, until I did a "umount -f" after several hours of debugging.

The internal state of this RPC client looks a little weird. I'm
attaching some debug output that shows where they got stuck. Some
general observation:

 -	this does not seem a queue corruption bug, which is good :)
 -	the tasks were sleeping on different wait queues (pending,
 	sending, 1 one resend)
 -	all tasks have a tk_timeout value of 0
 -	the ntimeo values of the RTT estimators being 0 looks a
	little weird, given that the mount froze because the
	server wasn't reachable.
 -	the task on the resend queue has a timer with
	tk_timer.expires != 0, but unfortunately I forgot to check whether
	it was active.	But I doubt it; I had debugging enabled for much
	of the day and the tk_pid in question never showed up in the log

I'm not sure yet what exactly happened here. I don't understand how a
task on xprt->pending can have a timeout value of 0...

Does anyone have an idea what might be going wrong here?

Olaf
-- 
Olaf Kirch     |  Stop wasting entropy - start using predictable
okir@suse.de   |  tempfile names today!
---------------+ 

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 Found NFS mount, server=Hilbert2,v3,rsize=8192,wsize=8192
   RPC client 6 users
     Active RPC tasks for this client:
       task 21384, status=-11, timeout=0, active, sleeping, on queue c45ea044(xprt_sending)
       task 9969, status=-11, timeout=0, active, sleeping, on queue c45ea044(xprt_sending)
       task 52431, status=-11, timeout=0, active, sleeping, on queue c45ea044(xprt_sending)
       task 43528, status=-11, timeout=0, active, sleeping, on queue c45ea044(xprt_sending)
       task 43527, status=-11, timeout=0, timer, async, active, sleeping, on queue c45ea050(xprt_resend)
       task 55816, status=0, timeout=0, active, sleeping, on queue c45ea05c(xprt_pending)
     Transport c45ea000, sockstate=0x1
       cong 256/cwnd 256
       RTT estimates (def timeout 700):
         0: rtt   15 srtt  100 ntimeo   0
         1: rtt   15 srtt  100 ntimeo   0
         2: rtt   49 srtt  100 ntimeo   0
         3: rtt   15 srtt  100 ntimeo   0
         4: rtt   15 srtt  100 ntimeo   0
     RPC wait queue sending:
       task 43528, status=-11, timeout=0, active, sleeping
       task 52431, status=-11, timeout=0, active, sleeping
       task 9969, status=-11, timeout=0, active, sleeping
       task 21384, status=-11, timeout=0, active, sleeping
     RPC wait queue pending:
       task 55816, status=0, timeout=0, active, sleeping
     RPC wait queue resend:
       task 43527, status=-11, timeout=0, active timer, async, active, sleeping
     RPC wait queue backlog: empty