[Nbd] deadlock in nbd?
I am trying to run nbd, without any luck: whatever I tried, I always
after a while had to reboot the (client) machine because of processes
stuck forever in uninteruptable sleep. This happens on several
different machines running different kernel versions (126.96.36.199,
188.8.131.52, 2.6.18-5 Debian Etch) and with different nbd versions
(2.9.7, 1:2.8.7-4 from Debian Etch).
I tried to isolate it from any networking peculiarities (All machines
use VLANs, most also interface bonding), but it seems that nbd
generally doesn't work over loppback interfaces. I also loaded the
module with "debugflags=0xffff" trying to get all possible debug
information, but the logged data looks pretty garbled (example:
<7quest c0f92e94: sending 4096 bytes data
<7uest e2c0fc90: sending 4096 bytes data
<7quest e3510c90: sending 4096 bytes data
) and when it is starting
to hang, nothing is logged. On the server side,
there generally aren't any errors in the syslog. So unfortunately,
I can't give a very detailed description. Here a pretty typical example
of what I am doing:
# server : # nbd-server 666 /dev/some/lvm/volume
# client : # nbd-client bs=4096 host 666 /dev/nbd0
# client : # mke2fs -j /dev/nbd0
Often, this will get stuck with the last message on the screen
"Writing superblocks and filesystem accounting information".
The mke2fs process is waiting on "sync_buffer", additionally
there are several pdflush threads stuck in "blk_congestion_wait".
Any ideas, what is going on and how to fix it?
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