Re: [Qemu-devel] [PATCH v11 for-4.0 09/11] qemu_thread: supplement error handling for migration

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Markus Armbruster (armbru@redhat.com) wrote:
> Dave, I tried to review the error paths, in particular resource cleanup,
> but there's a lot going on, and I'm not feeling confident.  Please have
> a close look.
> 
> Fei Li <lifei1214@126.com> writes:
> 
> > From: Fei Li <fli@suse.com>
> >
> > Update qemu_thread_create()'s callers by
> > - setting an error on qemu_thread_create() failure for callers that
> >   set an error on failure;
> > - reporting the error and returning failure for callers that return
> >   an error code on failure;
> > - reporting the error and setting some state for callers that just
> >   report errors and choose not to continue on.
> >
> > Besides, make compress_threads_save_cleanup() cope with partially
> > initialized comp_param[i] to adapt to the new qemu_thread_create()
> > failure case.
> >
> > Cc: Markus Armbruster <armbru@redhat.com>
> > Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > Signed-off-by: Fei Li <fli@suse.com>
> > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
> >  migration/migration.c    | 35 +++++++++++++-------
> >  migration/postcopy-ram.c | 16 ++++++---
> >  migration/ram.c          | 70 ++++++++++++++++++++++++++--------------
> >  migration/savevm.c       | 12 ++++---
> >  4 files changed, 89 insertions(+), 44 deletions(-)
> >
> > diff --git a/migration/migration.c b/migration/migration.c
> > index 1da71211c8..0034ca1334 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -447,10 +447,13 @@ static void process_incoming_migration_co(void *opaque)
> >              goto fail;
> >          }
> >  
> > -        /* TODO: let the further caller handle the error instead of abort() */
> > -        qemu_thread_create(&mis->colo_incoming_thread, "COLO incoming",
> > -                           colo_process_incoming_thread, mis,
> > -                           QEMU_THREAD_JOINABLE, &error_abort);
> > +        if (qemu_thread_create(&mis->colo_incoming_thread, "COLO incoming",
> > +                               colo_process_incoming_thread, mis,
> > +                               QEMU_THREAD_JOINABLE, &local_err) < 0) {
> > +            error_reportf_err(local_err, "failed to create "
> > +                              "colo_process_incoming_thread: ");
> > +            goto fail;
> > +        }
> >          mis->have_colo_incoming_thread = true;
> >          qemu_coroutine_yield();
> >  
> > @@ -2349,6 +2352,7 @@ out:
> >  static int open_return_path_on_source(MigrationState *ms,
> >                                        bool create_thread)
> >  {
> > +    Error *local_err = NULL;
> >  
> >      ms->rp_state.from_dst_file = qemu_file_get_return_path(ms->to_dst_file);
> >      if (!ms->rp_state.from_dst_file) {
> > @@ -2362,10 +2366,15 @@ static int open_return_path_on_source(MigrationState *ms,
> >          return 0;
> >      }
> >  
> > -    /* TODO: let the further caller handle the error instead of abort() here */
> > -    qemu_thread_create(&ms->rp_state.rp_thread, "return path",
> > -                       source_return_path_thread, ms,
> > -                       QEMU_THREAD_JOINABLE, &error_abort);
> > +    if (qemu_thread_create(&ms->rp_state.rp_thread, "return path",
> > +                           source_return_path_thread, ms,
> > +                           QEMU_THREAD_JOINABLE, &local_err) < 0) {
> > +        error_reportf_err(local_err,
> > +                          "failed to create source_return_path_thread: ");
> > +        qemu_fclose(ms->rp_state.from_dst_file);
> > +        ms->rp_state.from_dst_file = NULL;
> > +        return -1;
> > +     }
> >  
> >      trace_open_return_path_on_source_continue();
> >  
> > @@ -3201,9 +3210,13 @@ void migrate_fd_connect(MigrationState *s, Error *error_in)
>        if (multifd_save_setup() != 0) {
>            migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
>                              MIGRATION_STATUS_FAILED);
> >          migrate_fd_cleanup(s);
> >          return;
> >      }
> > -    /* TODO: let the further caller handle the error instead of abort() here */
> > -    qemu_thread_create(&s->thread, "live_migration", migration_thread, s,
> > -                       QEMU_THREAD_JOINABLE, &error_abort);
> > +    if (qemu_thread_create(&s->thread, "live_migration", migration_thread, s,
> > +                           QEMU_THREAD_JOINABLE, &error_in) < 0) {
> > +        error_reportf_err(error_in, "failed to create migration_thread: ");
> > +        migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED);
> > +        migrate_fd_cleanup(s);
> 
> Is there anything to clean up for multifd_save_setup()?  Dave?

I need to bounce that one to Juan; he knows the multifd stuff; cc'd

> > +        return;
> > +    }
> >      s->migration_thread_running = true;
> >  }
> >  
> > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> > index 221ea24919..0934a1403a 100644
> > --- a/migration/postcopy-ram.c
> > +++ b/migration/postcopy-ram.c
> > @@ -1083,6 +1083,8 @@ retry:
> >  
> >  int postcopy_ram_enable_notify(MigrationIncomingState *mis)
> >  {
> > +    Error *local_err = NULL;
> > +
> >      /* Open the fd for the kernel to give us userfaults */
> >      mis->userfault_fd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
> >      if (mis->userfault_fd == -1) {
> > @@ -1109,10 +1111,16 @@ int postcopy_ram_enable_notify(MigrationIncomingState *mis)
> >      }
> >  
> >      qemu_sem_init(&mis->fault_thread_sem, 0);
> > -    /* TODO: let the further caller handle the error instead of abort() here */
> > -    qemu_thread_create(&mis->fault_thread, "postcopy/fault",
> > -                       postcopy_ram_fault_thread, mis,
> > -                       QEMU_THREAD_JOINABLE, &error_abort);
> > +    if (qemu_thread_create(&mis->fault_thread, "postcopy/fault",
> > +                           postcopy_ram_fault_thread, mis,
> > +                           QEMU_THREAD_JOINABLE, &local_err) < 0) {
> > +        error_reportf_err(local_err,
> > +                          "failed to create postcopy_ram_fault_thread: ");
> > +        close(mis->userfault_event_fd);
> > +        close(mis->userfault_fd);
> > +        qemu_sem_destroy(&mis->fault_thread_sem);
> > +        return -1;
> > +    }
> >      qemu_sem_wait(&mis->fault_thread_sem);
> >      qemu_sem_destroy(&mis->fault_thread_sem);
> >      mis->have_fault_thread = true;
> 
>        /* Mark so that we get notified of accesses to unwritten areas */
>        if (qemu_ram_foreach_migratable_block(ram_block_enable_notify, mis)) {
>            error_report("ram_block_enable_notify failed");
>            return -1;
> 
> Not this patch's problem, but here goes anyway: where are
> mis->userfault_event_fd and mis->userfault_fd closed?

As Fei replied, see postcopy_ram_incoming_cleanup; once the fault thread
is running it does a bigger cleanup.

Dave

>        }
> 
> > diff --git a/migration/ram.c b/migration/ram.c
> > index 700ea229e0..66b8b764f1 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -441,6 +441,14 @@ static void compress_threads_save_cleanup(void)
> >  
> >      thread_count = migrate_compress_threads();
> >      for (i = 0; i < thread_count; i++) {
> > +        qemu_mutex_lock(&comp_param[i].mutex);
> > +        comp_param[i].quit = true;
> > +        qemu_cond_signal(&comp_param[i].cond);
> > +        qemu_mutex_unlock(&comp_param[i].mutex);
> > +
> > +        qemu_mutex_destroy(&comp_param[i].mutex);
> > +        qemu_cond_destroy(&comp_param[i].cond);
> > +
> >          /*
> >           * we use it as a indicator which shows if the thread is
> >           * properly init'd or not
> > @@ -448,15 +456,7 @@ static void compress_threads_save_cleanup(void)
> >          if (!comp_param[i].file) {
> >              break;
> >          }
> > -
> > -        qemu_mutex_lock(&comp_param[i].mutex);
> > -        comp_param[i].quit = true;
> > -        qemu_cond_signal(&comp_param[i].cond);
> > -        qemu_mutex_unlock(&comp_param[i].mutex);
> > -
> >          qemu_thread_join(compress_threads + i);
> > -        qemu_mutex_destroy(&comp_param[i].mutex);
> > -        qemu_cond_destroy(&comp_param[i].cond);
> >          deflateEnd(&comp_param[i].stream);
> >          g_free(comp_param[i].originbuf);
> >          qemu_fclose(comp_param[i].file);
> > @@ -473,6 +473,7 @@ static void compress_threads_save_cleanup(void)
> >  static int compress_threads_save_setup(void)
> >  {
> >      int i, thread_count;
> > +    Error *local_err = NULL;
> >  
> >      if (!migrate_use_compression()) {
> >          return 0;
> > @@ -483,6 +484,9 @@ static int compress_threads_save_setup(void)
> >      qemu_cond_init(&comp_done_cond);
> >      qemu_mutex_init(&comp_done_lock);
> >      for (i = 0; i < thread_count; i++) {
> > +        qemu_mutex_init(&comp_param[i].mutex);
> > +        qemu_cond_init(&comp_param[i].cond);
> > +        comp_param[i].quit = false;
> >          comp_param[i].originbuf = g_try_malloc(TARGET_PAGE_SIZE);
> >          if (!comp_param[i].originbuf) {
> >              goto exit;
> > @@ -499,13 +503,16 @@ static int compress_threads_save_setup(void)
> >           */
> >          comp_param[i].file = qemu_fopen_ops(NULL, &empty_ops);
> >          comp_param[i].done = true;
> > -        comp_param[i].quit = false;
> > -        qemu_mutex_init(&comp_param[i].mutex);
> > -        qemu_cond_init(&comp_param[i].cond);
> > -        /* TODO: let the further caller handle the error instead of abort() */
> > -        qemu_thread_create(compress_threads + i, "compress",
> > -                           do_data_compress, comp_param + i,
> > -                           QEMU_THREAD_JOINABLE, &error_abort);
> > +        if (qemu_thread_create(compress_threads + i, "compress",
> > +                               do_data_compress, comp_param + i,
> > +                               QEMU_THREAD_JOINABLE, &local_err) < 0) {
> > +            error_reportf_err(local_err, "failed to create do_data_compress: ");
> > +            deflateEnd(&comp_param[i].stream);
> > +            g_free(comp_param[i].originbuf);
> > +            qemu_fclose(comp_param[i].file);
> > +            comp_param[i].file = NULL;
> > +            goto exit;
> > +        }
> >      }
> >      return 0;
> >  
> > @@ -1076,9 +1083,14 @@ static void multifd_new_send_channel_async(QIOTask *task, gpointer opaque)
> >          p->c = QIO_CHANNEL(sioc);
> >          qio_channel_set_delay(p->c, false);
> >          p->running = true;
> > -        /* TODO: let the further caller handle the error instead of abort() */
> > -        qemu_thread_create(&p->thread, p->name, multifd_send_thread, p,
> > -                           QEMU_THREAD_JOINABLE, &error_abort);
> > +        if (qemu_thread_create(&p->thread, p->name, multifd_send_thread, p,
> > +                               QEMU_THREAD_JOINABLE, &local_err) < 0) {
> > +            migrate_set_error(migrate_get_current(), local_err);
> > +            error_reportf_err(local_err,
> > +                              "failed to create multifd_send_thread: ");
> > +            multifd_save_cleanup();
> > +            return;
> > +        }
> >  
> >          atomic_inc(&multifd_send_state->count);
> >      }
> > @@ -1357,9 +1369,13 @@ bool multifd_recv_new_channel(QIOChannel *ioc, Error **errp)
> >      p->num_packets = 1;
> >  
> >      p->running = true;
> > -    /* TODO: let the further caller handle the error instead of abort() here */
> > -    qemu_thread_create(&p->thread, p->name, multifd_recv_thread, p,
> > -                       QEMU_THREAD_JOINABLE, &error_abort);
> > +    if (qemu_thread_create(&p->thread, p->name, multifd_recv_thread, p,
> > +                           QEMU_THREAD_JOINABLE, &local_err) < 0) {
> > +        error_propagate_prepend(errp, local_err,
> > +                                "failed to create multifd_recv_thread: ");
> 
> This prepends only if @errp isn't null.  Fine from the caller's point of
> view.  But it also affects multifd_recv_thread():
> 
> > +        multifd_recv_terminate_threads(local_err);
> 
> That's at least unclean.
> 
> I think you should use error_prepend() and error_propagate() here.
> 
> > +        return false;
> > +    }
> >      atomic_inc(&multifd_recv_state->count);
> >      return atomic_read(&multifd_recv_state->count) ==
> >             migrate_multifd_channels();
> > @@ -3631,6 +3647,7 @@ static void compress_threads_load_cleanup(void)
> >  static int compress_threads_load_setup(QEMUFile *f)
> >  {
> >      int i, thread_count;
> > +    Error *local_err = NULL;
> >  
> >      if (!migrate_use_compression()) {
> >          return 0;
> > @@ -3652,10 +3669,13 @@ static int compress_threads_load_setup(QEMUFile *f)
> >          qemu_cond_init(&decomp_param[i].cond);
> >          decomp_param[i].done = true;
> >          decomp_param[i].quit = false;
> > -        /* TODO: let the further caller handle the error instead of abort() */
> > -        qemu_thread_create(decompress_threads + i, "decompress",
> > -                           do_data_decompress, decomp_param + i,
> > -                           QEMU_THREAD_JOINABLE, &error_abort);
> > +        if (qemu_thread_create(decompress_threads + i, "decompress",
> > +                               do_data_decompress, decomp_param + i,
> > +                               QEMU_THREAD_JOINABLE, &local_err) < 0) {
> > +            error_reportf_err(local_err,
> > +                              "failed to create do_data_decompress: ");
> > +            goto exit;
> > +        }
> >      }
> >      return 0;
> >  exit:
> > diff --git a/migration/savevm.c b/migration/savevm.c
> > index d5b45843b6..310cecbf8f 100644
> > --- a/migration/savevm.c
> > +++ b/migration/savevm.c
> > @@ -1747,10 +1747,14 @@ static int loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
> >      mis->have_listen_thread = true;
> >      /* Start up the listening thread and wait for it to signal ready */
> >      qemu_sem_init(&mis->listen_thread_sem, 0);
> > -    /* TODO: let the further caller handle the error instead of abort() here */
> > -    qemu_thread_create(&mis->listen_thread, "postcopy/listen",
> > -                       postcopy_ram_listen_thread, NULL,
> > -                       QEMU_THREAD_DETACHED, &error_abort);
> > +    if (qemu_thread_create(&mis->listen_thread, "postcopy/listen",
> > +                           postcopy_ram_listen_thread, NULL,
> > +                           QEMU_THREAD_DETACHED, &local_err) < 0) {
> > +        error_reportf_err(local_err,
> > +                          "failed to create postcopy_ram_listen_thread: ");
> > +        qemu_sem_destroy(&mis->listen_thread_sem);
> > +        return -1;
> > +    }
> >      qemu_sem_wait(&mis->listen_thread_sem);
> >      qemu_sem_destroy(&mis->listen_thread_sem);
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK