[Qemu-devel] Re: [PATCH 0/2] avoid races on exec migration

[Paolo Bonzini <pbonzini@redhat.com>]

On 03/09/2011 06:21 PM, Paolo Bonzini wrote:
> QEMU has a sigchld handler that reaps any child process.  -smb is the
> only user of it and, in fact, QEMU inherited it from slirp.  However,
> this handler causes 'exec' based migration to randomly return 'status:
> failed' in the monitor.  This happens when the signal handler for SIGCHLD
> is ran before the pclose() of exec migration.
>
> The return status of fclose() is passed back as return status of
> qemu_fclose().  If qemu_fclose() fails, then the exec_close() in
> migration-exec.c returns a error code. This causes migrate_fd_cleanup()
> to return an error, and thus finally we see why 'status: failed' occurs:
>
>          if (migrate_fd_cleanup(s)<  0) {
>              if (old_vm_running) {
>                  vm_start();
>              }
>              state = MIG_STATE_ERROR;
>          }
>
> To avoid this, register the pids in a list and, on SIGCHLD, set up a
> bottom-half that would go through the pids and reap them.
>
> Since I'm at it, I'm moving iohandler stuff out of vl.c.  The new
> file isn't a perfect place to add the child watcher, but it's arguably
> better than vl.c.
>
> This should be applied to both master and stable.
>
> Paolo Bonzini (2):
>    extract I/O handler lists to iohandler.c
>    add a service to reap zombies
>
>   Makefile.objs |    2 +-
>   iohandler.c   |  193 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   os-posix.c    |    9 ---
>   qemu-common.h |    4 +
>   slirp/misc.c  |    5 +-
>   vl.c          |  106 ++------------------------------
>   6 files changed, 207 insertions(+), 112 deletions(-)
>   create mode 100644 iohandler.c
>

Ping?

Paolo