| Message ID | 20191010011316.31363-3-richardw.yang@linux.intel.com |
|---|---|
| State | New |
| Headers | show |
| Series | migration/postcopy: cleanup related to postcopy | expand |
* Wei Yang (richardw.yang@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 checking the state first. > > Signed-off-by: Wei Yang <richardw.yang@linux.intel.com> > Suggested by: Peter Xu <peterx@redhat.com> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> > --- > migration/savevm.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/migration/savevm.c b/migration/savevm.c > index 78c2965ca4..b9f30a7090 100644 > --- a/migration/savevm.c > +++ b/migration/savevm.c > @@ -1934,7 +1934,7 @@ static void loadvm_postcopy_handle_run_bh(void *opaque) > /* After all discards we can start running and asking for pages */ > static int loadvm_postcopy_handle_run(MigrationIncomingState *mis) > { > - PostcopyState ps = postcopy_state_set(POSTCOPY_INCOMING_RUNNING); > + PostcopyState ps = postcopy_state_get(); > > trace_loadvm_postcopy_handle_run(); > if (ps != POSTCOPY_INCOMING_LISTENING) { > @@ -1942,6 +1942,7 @@ static int loadvm_postcopy_handle_run(MigrationIncomingState *mis) > return -1; > } > > + postcopy_state_set(POSTCOPY_INCOMING_RUNNING); > mis->bh = qemu_bh_new(loadvm_postcopy_handle_run_bh, mis); > qemu_bh_schedule(mis->bh); > > -- > 2.17.1 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
diff --git a/migration/savevm.c b/migration/savevm.c index 78c2965ca4..b9f30a7090 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -1934,7 +1934,7 @@ static void loadvm_postcopy_handle_run_bh(void *opaque) /* After all discards we can start running and asking for pages */ static int loadvm_postcopy_handle_run(MigrationIncomingState *mis) { - PostcopyState ps = postcopy_state_set(POSTCOPY_INCOMING_RUNNING); + PostcopyState ps = postcopy_state_get(); trace_loadvm_postcopy_handle_run(); if (ps != POSTCOPY_INCOMING_LISTENING) { @@ -1942,6 +1942,7 @@ static int loadvm_postcopy_handle_run(MigrationIncomingState *mis) return -1; } + postcopy_state_set(POSTCOPY_INCOMING_RUNNING); mis->bh = qemu_bh_new(loadvm_postcopy_handle_run_bh, mis); qemu_bh_schedule(mis->bh);
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> --- migration/savevm.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)