On Wed, Oct 09, 2019 at 01:36:34PM +0800, Peter Xu wrote: >On Wed, Oct 09, 2019 at 01:07:56PM +0800, Wei Yang wrote: >> On Wed, Oct 09, 2019 at 12:12:25PM +0800, Peter Xu wrote: >> >On Wed, Oct 09, 2019 at 09:02:04AM +0800, Wei Yang wrote: >> >> On Tue, Oct 08, 2019 at 05:40:46PM +0100, Dr. David Alan Gilbert wrote: >> >> >* Wei Yang (richardw.y...@linux.intel.com) wrote: >> >> >> 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 introducing an old_state parameter in >> >> >> postcopy_state_set(). >> >> >> New state only would be set when current state equals to old_state. >> >> >> >> >> >> Signed-off-by: Wei Yang <richardw.y...@linux.intel.com> >> >> > >> >> >OK, it's a shame to use a pointer there, but it works. >> >> >> >> You mean second parameter of postcopy_state_set()? >> >> >> >> I don't have a better idea. Or we introduce a new state >> >> POSTCOPY_INCOMING_NOCHECK. Do you feel better with this? >> > >> >Maybe simply fix loadvm_postcopy_handle_run() to set the state after >> >the POSTCOPY_INCOMING_LISTENING check? >> > >> >> Set state back to ps if ps is not POSTCOPY_INCOMING_LISTENING? >> >> Sounds like another option. > >Even simpler? > > ps = postcopy_state_get(); > if (ps != INCOMING) > return -1; > postcopy_state_set(RUNNING); >
Looks good to me. Dave, Do you feel good with it? >Thanks, > >-- >Peter Xu -- Wei Yang Help you, Help me