04.08.2011 23:24, Luiz Capitulino пишет:
> On Wed, 3 Aug 2011 18:51:44 +0400
> Michael Tokarev <m...@tls.msk.ru> wrote:
>
>> If we do, it results in double monitor_resume() (second being called
>> from migrate_fd_cleanup() anyway) and monitor suspend count becoming
>> negative.
>
> Are you hitting an specific issue or did you find this by code inspection?
The specific case I'm talking about can trivially be triggered.
Run migrate "exec:nosuchfile" and your monitor will be stuck
forever.
> IIRC, I asked Marcelo to add the monitor_resume() call in the fix for
> e447b1a603 because the monitor wasn't being resumed in some cases. Don't
> remember which though, do you Marcelo?
And this (e447b1a603) is actually exactly the same thing: when the
child terminates before qemu completes sending stuff to it.
> I see two possibilities here:
>
> 1. After e447b1a603 there was some change that made the monitor_resume() call
> in migrate_fd_put_buffer() unnecessary
>
> 2. We're calling it in the wrong place
>
> Taking a quick look at the code I see that migrate_fd_cleanup() doesn't
> seem to be called when qemu_savevm_state_iterate() fails, for example.
Yes indeed, but that will lead to a havoc in other places, like
leaving callback notifier registered even after migration gets
cancelled, or keeping the file open.
Note that qemu_savevm_state_iterate() gets called from a callback
routine.
What I observe here is that when the exec: process exits prematurely,
qemu will continue writing stuff to pipe up till migrate_fd_put_buffer()
hits error (EPIPE iirc), at which point we'll call mon->resume() twice.
The same happens in case of tcp migration when the other end closes
the connection.
I don't know when qemu_savevm_state_iterate() may fail, or why
qemu_file_has_error() in there does not return true.
Maybe the problem here is much more severe actually, -- that's why
I initially asked what it is all about, -- before offering the patch.
Thanks,
/mjt
>> Signed-Off-By: Michael Tokarev <m...@tls.msk.ru>
>> Reviewed-By: Jan Kiszka <jan.kis...@siemens.com>
>> ---
>> migration.c | 3 ---
>> 1 files changed, 0 insertions(+), 3 deletions(-)
>>
>> diff --git a/migration.c b/migration.c
>> index 2a15b98..7ca883f 100644
>> --- a/migration.c
>> +++ b/migration.c
>> @@ -330,9 +330,6 @@ ssize_t migrate_fd_put_buffer(void *opaque, const void
>> *data, size_t size)
>> if (ret == -EAGAIN) {
>> qemu_set_fd_handler2(s->fd, NULL, NULL, migrate_fd_put_notify, s);
>> } else if (ret < 0) {
>> - if (s->mon) {
>> - monitor_resume(s->mon);
>> - }
>> s->state = MIG_STATE_ERROR;
>> notifier_list_notify(&migration_state_notifiers, NULL);
>> }
>
