This bug has also been reproduced with a tar-pipe-tar process, using 

ssh remote tar cfP - /path/to/dir | tar xf -


After some investigation, it seems there is an issue with the ssh process. When the rsync process is stuck in state 'D', the ssh process is in state 'S+':


client:
=================
root       651  0.0  0.0  49252  1080 ?        Ss   09:53   0:00 /usr/sbin/sshd
root      2681  0.0  0.0  70572  3308 ?        Ss   09:53   0:00  \_ sshd: root@pts/0 
root      2693  0.0  0.0  19340  3496 pts/0    Ss   09:53   0:00  |   \_ -bash
root      8210  0.6  0.0   4328   800 pts/0    S+   10:00   0:12  |       \_ strace rsync -av --ignore-existing gforge01.vprod.infra.s1.p.fti.net:/var/lib/mailman/ /var/lib/mailman
root      8211  0.2  0.3 124076 14536 pts/0    D+   10:00   0:04  |           \_ rsync -av --ignore-existing gforge01.vprod.infra.s1.p.fti.net:/var/lib/mailman/ /var/lib/mailman
root      8212  5.0  0.1  44556  6756 pts/0    S+   10:00   1:39  |               \_ ssh gforge01.vprod.infra.s1.p.fti.net rsync --server --sender -vlogDtpre.iLsf . /var/lib/mailman/
root      8213  3.3  0.4 285744 19876 pts/0    D+   10:00   1:05  |               \_ rsync -av --ignore-existing gforge01.vprod.infra.s1.p.fti.net:/var/lib/mailman/ /var/lib/mailman
=================


server:
=================
root     26107  5.4  0.2  13452  6616 ?        Ss   10:00   1:55  \_ sshd: root@notty 
root     26154  2.5  1.3  93880 41428 ?        Ss   10:00   0:54  |   \_ rsync --server --sender -vlogDtpre.iLsf . /var/lib/mailman/
=================



The strace track on the ssh process on both sides of the network link show that the processes try to access file descriptors that are not listed in /proc:


client:
=================
root@mail01:/var/log# strace -p 8212
Process 8212 attached - interrupt to quit
select(7, [3 4], [5], NULL, NULL

root@mail01:/var/log# ls -l /proc/8212/fd
total 0
lrwx------ 1 root root 64 May 20 10:28 0 -> socket:[11967]
lrwx------ 1 root root 64 May 20 10:28 1 -> socket:[11970]
l-wx------ 1 root root 64 May 20 10:16 2 -> /var/log/rsync_strace
lrwx------ 1 root root 64 May 20 10:28 3 -> socket:[11980]
lrwx------ 1 root root 64 May 20 10:28 4 -> socket:[11967]
lrwx------ 1 root root 64 May 20 10:28 5 -> socket:[11970]
l-wx------ 1 root root 64 May 20 10:28 6 -> /var/log/rsync_strace
=================


server:
=================
[PROD/MASTER] gforge01:~# strace -p 26107
Process 26107 attached - interrupt to quit
select(14, [3 6], [], NULL, NULL

[PROD/MASTER] gforge01:~# ls -l /proc/26107/fd/
total 0
lrwx------ 1 root root 64 2010-05-20 10:36 0 -> /dev/null
lrwx------ 1 root root 64 2010-05-20 10:36 1 -> /dev/null
l-wx------ 1 root root 64 2010-05-20 10:36 10 -> pipe:[4066236232]
lr-x------ 1 root root 64 2010-05-20 10:36 11 -> pipe:[4066236233]
lr-x------ 1 root root 64 2010-05-20 10:36 13 -> pipe:[4066236234]
lrwx------ 1 root root 64 2010-05-20 10:36 2 -> /dev/null
lrwx------ 1 root root 64 2010-05-20 10:36 3 -> socket:[4066235605]
lrwx------ 1 root root 64 2010-05-20 10:36 4 -> socket:[4066235803]
lrwx------ 1 root root 64 2010-05-20 10:36 5 -> socket:[4066236227]
lr-x------ 1 root root 64 2010-05-20 10:36 6 -> pipe:[4066236229]
lr-x------ 1 root root 64 2010-05-20 10:36 7 -> /dev/urandom
l-wx------ 1 root root 64 2010-05-20 10:36 8 -> pipe:[4066236229]
=================