Re: kern/42455: tstile hang with nfs

["Christoph Egger" <Christoph_Egger%gmx.de@localhost>]

I added debug printf's right before every 'goto nfsmout'
in the macros.

When the bug happened again I saw none of the debug printf's.

I also printed the 'mb' address and in ddb 'show mbuf' says:

db> show mbuf 0xffffa00001170400
MBUF 0xffffa00001170400
  data=0xffffa000011a2802, len=2046, type=1, flags=0x0x9000003<EXT,PKTHDR,
EXT_CLUSTER,EXT_RW>
  owner=0x0, next=0x0, nextpkt=0x0
  leadingspace=2, trailingspace=0, readonly=0
  pktlen=2046, rcvif=0x0, csum_flags=0x0x0, csum_data=0x0, segsz=402653184
  ext_refcnt=1, ext_buf=0xffffa000011a2800, ext_size=2048, ext_free=0x0,
ext_arg=0xffffa0002320d3d0

next=0x0 => mb is not a chained mbuf.

nwc.mbuf_count is initialized with 1
and nwc.mbuf_count is decreased by one right before it enters
the while loop with 'cv_wait' so nwc.mbuf_count must have
been 2 before it entered the loop.

There is only one way to increase nwc.mbuf_count: it must run
the path where MEXTADD() is used which chains an mbuf to 'mb'.

Christoph