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

[Paolo Bonzini <pbonzini@redhat.com>]

On 03/21/2011 09:24 AM, Paolo Bonzini wrote:
> 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?

Ping^2?

Paolo