Re: [PATCH v2] migration: Stop migration immediately in RDMA error paths

[Juan Quintela]

Peter Xu <peterx@redhat.com> wrote:
> On Tue, Oct 24, 2023 at 06:16:27PM +0200, Juan Quintela wrote:
>> Peter Xu <peterx@redhat.com> wrote:
>> > In multiple places, RDMA errors are handled in a strange way, where it only
>> > sets qemu_file_set_error() but not stop the migration immediately.
>> >
>> > It's not obvious what will happen later if there is already an error.  Make
>> > all such failures stop migration immediately.
>> >
>> > Cc: Zhijian Li (Fujitsu) <lizhijian@fujitsu.com>
>> > Cc: Markus Armbruster <armbru@redhat.com>
>> > Cc: Juan Quintela <quintela@redhat.com>
>> > Cc: Fabiano Rosas <farosas@suse.de>
>> > Reported-by: Thomas Huth <thuth@redhat.com>
>> > Signed-off-by: Peter Xu <peterx@redhat.com>
>> > ---
>> >
>> > v2:
>> > - One more line squashed into to fix the build error...  Please ignore v1,
>> >   sorry for the noise.
>> >
>> > This patch is based on Thomas's patch:
>> >
>> > [PATCH v2] migration/ram: Fix compilation with -Wshadow=local
>> > 20231024092220.55305-1-thuth@redhat.com">https://lore.kernel.org/r/20231024092220.55305-1-thuth@redhat.com
>> >
>> > Above patch should have been queued by both Markus and Juan.
>> > ---
>> >  migration/ram.c | 13 ++++++++-----
>> >  1 file changed, 8 insertions(+), 5 deletions(-)
>> >
>> > diff --git a/migration/ram.c b/migration/ram.c
>> > index 212add4481..1473bb593a 100644
>> > --- a/migration/ram.c
>> > +++ b/migration/ram.c
>> > @@ -3034,11 +3034,13 @@ static int ram_save_setup(QEMUFile *f, void 
>> > *opaque)
>> >      ret = rdma_registration_start(f, RAM_CONTROL_SETUP);
>> >      if (ret < 0) {
>> >          qemu_file_set_error(f, ret);
>> > +        return ret;
>> 
>> I agree
>> 
>> >      }
>> >  
>> >      ret = rdma_registration_stop(f, RAM_CONTROL_SETUP);
>> >      if (ret < 0) {
>> >          qemu_file_set_error(f, ret);
>> > +        return ret;
>> 
>> I agree
>> 
>> >      }
>> >  
>> >      migration_ops = g_malloc0(sizeof(MigrationOps));
>> > @@ -3104,6 +3106,7 @@ static int ram_save_iterate(QEMUFile *f, void 
>> > *opaque)
>> >          ret = rdma_registration_start(f, RAM_CONTROL_ROUND);
>> >          if (ret < 0) {
>> >              qemu_file_set_error(f, ret);
>> > +            goto out;
>> 
>> Seems sensible
>> 
>> >          }
>> >  
>> >          t0 = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
>> > @@ -3208,8 +3211,6 @@ static int ram_save_complete(QEMUFile *f, void 
>> > *opaque)
>> >      rs->last_stage = !migration_in_colo_state();
>> >  
>> >      WITH_RCU_READ_LOCK_GUARD() {
>> > -        int rdma_reg_ret;
>> > -
>> >          if (!migration_in_postcopy()) {
>> >              migration_bitmap_sync_precopy(rs, true);
>> >          }
>> > @@ -3217,6 +3218,7 @@ static int ram_save_complete(QEMUFile *f, void 
>> > *opaque)
>> >          ret = rdma_registration_start(f, RAM_CONTROL_FINISH);
>> >          if (ret < 0) {
>> >              qemu_file_set_error(f, ret);
>> > +            break;
>> 
>> Please
>>               return ret;
>> 
>> 
>> We can do exactly the same with pages < 0.
>> 
>> >          }
>> >  
>> >          /* try transferring iterative blocks of memory */
>> > @@ -3240,9 +3242,10 @@ static int ram_save_complete(QEMUFile *f, void 
>> > *opaque)
>> >  
>> >          ram_flush_compressed_data(rs);
>> >  
>> > -        rdma_reg_ret = rdma_registration_stop(f, RAM_CONTROL_FINISH);
>> > -        if (rdma_reg_ret < 0) {
>> > -            qemu_file_set_error(f, rdma_reg_ret);
>> > +        ret = rdma_registration_stop(f, RAM_CONTROL_FINISH);
>> > +        if (ret < 0) {
>> > +            qemu_file_set_error(f, ret);
>> > +            break;
>> >          }
>> >      }
>> 
>> And if we return here, we can just drop the:
>> 
>>     if (ret < 0) {
>>         return ret;
>>     }
>> 
>> 
>> At the ext of the loop.
>
> IIUC that'll be the same as this patch,

No.

if you see a break, you need to search for the loop, and go to the end
and see what happens.

  return ret;

It is completely obvious what we do in case of error.

> but sure thing I'll prepare a v3.

Thanks.