[libvirt] "Unable to read QEMU help output: Interrupted system call" doing virDomainRestore() on current master

[Charles Duffy]

Howdy. I've had this issue since yesterday, but avoided reporting it 
until determining today that it occurs on an unmodified upstream tree as 
well as my own local branch:

$ virsh restore ramsave
error: Failed to restore domain from ramsave
error: Unable to read QEMU help output: Interrupted system call

This happens immediately (no delay) and only on restore; "virsh start" 
behaves as usual.


When running libvirtd under gdb, the failure mode is different:

$ virsh restore ramsave
error: Failed to restore domain from ramsave
error: internal error Timed out while reading monitor startup output


When running libvirtd under strace, this shows the binary being run 
(["/usr/bin/qemu-kvm", "-help"]) failing with a SIGPIPE while attempting 
to write to stdout. strace also shows a SIGSEGV being delivered to a 
libvirtd thread (a few clone()s removed from the parent) after that 
thread attempts to close all its open file descriptors above 0-2, but 
without being able to run gdb I'm at a bit of a loss as to what that 
thread is doing.


Any suggestions?