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[Xen-devel] "xm save" trouble -- deadlock?

To: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] "xm save" trouble -- deadlock?
From: Gerd Knorr <kraxel@xxxxxxx>
Date: Tue, 01 Nov 2005 17:43:56 +0100
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  Hi,

"xm save" doesn't work for me, the command just blocks forever. In the process list it looks like this:

 6567 ?        Ssl    0:00 python /usr/sbin/xend restart
 7978 ?        SL     0:00  \_ /usr/lib/xen/bin/xc_save 14 17 10 0 0 0

xc_save is blocked, in a write call to stderr:

  master-xen root /vm/ttylinux# strace -p7978
  Process 7978 attached - interrupt to quit
  write(2, "FNI 28 : [10000004,815] pte=2b92"..., 80 <unfinished ...>
  Process 7978 detached

stderr is a pipe to xend:

  master-xen root /vm/ttylinux# ll /proc/7978/fd/2
  l-wx------  1 root root 64 Nov  1 17:25 /proc/7978/fd/2 -> pipe:[40419]
  master-xen root /vm/ttylinux# ll /proc/*/fd/* | grep 40419
  lr-x------  1 root root 64 Nov  1 17:25 /proc/6567/fd/22 -> pipe:[40419]
  l-wx------  1 root root 64 Nov  1 17:25 /proc/7978/fd/2 -> pipe:[40419]

xend in turn doesn't read from the pipe but is waiting for some lock:

  master-xen root /vm/ttylinux# strace -p6567
  Process 6567 attached - interrupt to quit
  futex(0x8087370, FUTEX_WAIT, 0, NULL <unfinished ...>
  Process 6567 detached

Ideas anyone what is going on here?

  Gerd

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