migration/postcopy: check PostcopyState before setting to POSTCOPY_INCOMING_RUNNING
commit0197d89025d768f3a2505ea50816fbc6b161b992
authorWei Yang <richardw.yang@linux.intel.com>
Thu, 10 Oct 2019 01:13:16 +0000 (10 09:13 +0800)
committerDr. David Alan Gilbert <dgilbert@redhat.com>
Fri, 11 Oct 2019 14:00:16 +0000 (11 15:00 +0100)
tree491e365cc695235f9f8dd2ce25dc92967866ce81
parent2a7eb14844c1b71df58aa980f7253bddc6f11676
migration/postcopy: check PostcopyState before setting to POSTCOPY_INCOMING_RUNNING

Currently, we set PostcopyState blindly to RUNNING, even we found the
previous state is not LISTENING. This will lead to a corner case.

First let's look at the code flow:

qemu_loadvm_state_main()
    ret = loadvm_process_command()
        loadvm_postcopy_handle_run()
            return -1;
    if (ret < 0) {
        if (postcopy_state_get() == POSTCOPY_INCOMING_RUNNING)
            ...
    }

>From above snippet, the corner case is loadvm_postcopy_handle_run()
always sets state to RUNNING. And then it checks the previous state. If
the previous state is not LISTENING, it will return -1. But at this
moment, PostcopyState is already been set to RUNNING.

Then ret is checked in qemu_loadvm_state_main(), when it is -1
PostcopyState is checked. Current logic would pause postcopy and retry
if PostcopyState is RUNNING. This is not what we expect, because
postcopy is not active yet.

This patch makes sure state is set to RUNNING only previous state is
LISTENING by checking the state first.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Suggested by: Peter Xu <peterx@redhat.com>
Message-Id: <20191010011316.31363-3-richardw.yang@linux.intel.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
migration/savevm.c