Re: [Qemu-devel] [PATCH v5 04/10] migration: implement bi-directional RDMA QIOChannel

[Dr. David Alan Gilbert]

* Lidong Chen (address@hidden) wrote:
> From: Lidong Chen <address@hidden>
> 
> This patch implements bi-directional RDMA QIOChannel. Because different
> threads may access RDMAQIOChannel currently, this patch use RCU to protect it.
> 
> Signed-off-by: Lidong Chen <address@hidden>

Paolo: Does it make sense the way RCU is used here  Holding the
read-lock for so long in multifd_rdma_[read|write]v is what worries me
most.  

Dave

> ---
>  migration/colo.c         |   2 +
>  migration/migration.c    |   2 +
>  migration/postcopy-ram.c |   2 +
>  migration/ram.c          |   4 +
>  migration/rdma.c         | 196 
> ++++++++++++++++++++++++++++++++++++++++-------
>  migration/savevm.c       |   3 +
>  6 files changed, 183 insertions(+), 26 deletions(-)
> 
> diff --git a/migration/colo.c b/migration/colo.c
> index 4381067..88936f5 100644
> --- a/migration/colo.c
> +++ b/migration/colo.c
> @@ -534,6 +534,7 @@ void *colo_process_incoming_thread(void *opaque)
>      uint64_t value;
>      Error *local_err = NULL;
>  
> +    rcu_register_thread();
>      qemu_sem_init(&mis->colo_incoming_sem, 0);
>  
>      migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
> @@ -666,5 +667,6 @@ out:
>      }
>      migration_incoming_exit_colo();
>  
> +    rcu_unregister_thread();
>      return NULL;
>  }
> diff --git a/migration/migration.c b/migration/migration.c
> index 1d0aaec..4253d9f 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -2028,6 +2028,7 @@ static void *source_return_path_thread(void *opaque)
>      int res;
>  
>      trace_source_return_path_thread_entry();
> +    rcu_register_thread();
>  
>  retry:
>      while (!ms->rp_state.error && !qemu_file_get_error(rp) &&
> @@ -2167,6 +2168,7 @@ out:
>      trace_source_return_path_thread_end();
>      ms->rp_state.from_dst_file = NULL;
>      qemu_fclose(rp);
> +    rcu_unregister_thread();
>      return NULL;
>  }
>  
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 48e5155..98613eb 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -853,6 +853,7 @@ static void *postcopy_ram_fault_thread(void *opaque)
>      RAMBlock *rb = NULL;
>  
>      trace_postcopy_ram_fault_thread_entry();
> +    rcu_register_thread();
>      mis->last_rb = NULL; /* last RAMBlock we sent part of */
>      qemu_sem_post(&mis->fault_thread_sem);
>  
> @@ -1059,6 +1060,7 @@ retry:
>              }
>          }
>      }
> +    rcu_unregister_thread();
>      trace_postcopy_ram_fault_thread_exit();
>      g_free(pfd);
>      return NULL;
> diff --git a/migration/ram.c b/migration/ram.c
> index a500015..a674fb5 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -683,6 +683,7 @@ static void *multifd_send_thread(void *opaque)
>      MultiFDSendParams *p = opaque;
>      Error *local_err = NULL;
>  
> +    rcu_register_thread();
>      if (multifd_send_initial_packet(p, &local_err) < 0) {
>          goto out;
>      }
> @@ -706,6 +707,7 @@ out:
>      p->running = false;
>      qemu_mutex_unlock(&p->mutex);
>  
> +    rcu_unregister_thread();
>      return NULL;
>  }
>  
> @@ -819,6 +821,7 @@ static void *multifd_recv_thread(void *opaque)
>  {
>      MultiFDRecvParams *p = opaque;
>  
> +    rcu_register_thread();
>      while (true) {
>          qemu_mutex_lock(&p->mutex);
>          if (p->quit) {
> @@ -833,6 +836,7 @@ static void *multifd_recv_thread(void *opaque)
>      p->running = false;
>      qemu_mutex_unlock(&p->mutex);
>  
> +    rcu_unregister_thread();
>      return NULL;
>  }
>  
> diff --git a/migration/rdma.c b/migration/rdma.c
> index f6705a3..769f443 100644
> --- a/migration/rdma.c
> +++ b/migration/rdma.c
> @@ -86,6 +86,7 @@ static uint32_t known_capabilities = 
> RDMA_CAPABILITY_PIN_ALL;
>                                  " to abort!"); \
>                  rdma->error_reported = 1; \
>              } \
> +            rcu_read_unlock(); \
>              return rdma->error_state; \
>          } \
>      } while (0)
> @@ -402,7 +403,8 @@ typedef struct QIOChannelRDMA QIOChannelRDMA;
>  
>  struct QIOChannelRDMA {
>      QIOChannel parent;
> -    RDMAContext *rdma;
> +    RDMAContext *rdmain;
> +    RDMAContext *rdmaout;
>      QEMUFile *file;
>      bool blocking; /* XXX we don't actually honour this yet */
>  };
> @@ -2630,12 +2632,20 @@ static ssize_t qio_channel_rdma_writev(QIOChannel 
> *ioc,
>  {
>      QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(ioc);
>      QEMUFile *f = rioc->file;
> -    RDMAContext *rdma = rioc->rdma;
> +    RDMAContext *rdma;
>      int ret;
>      ssize_t done = 0;
>      size_t i;
>      size_t len = 0;
>  
> +    rcu_read_lock();
> +    rdma = atomic_rcu_read(&rioc->rdmaout);
> +
> +    if (!rdma) {
> +        rcu_read_unlock();
> +        return -EIO;
> +    }
> +
>      CHECK_ERROR_STATE();
>  
>      /*
> @@ -2645,6 +2655,7 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
>      ret = qemu_rdma_write_flush(f, rdma);
>      if (ret < 0) {
>          rdma->error_state = ret;
> +        rcu_read_unlock();
>          return ret;
>      }
>  
> @@ -2664,6 +2675,7 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
>  
>              if (ret < 0) {
>                  rdma->error_state = ret;
> +                rcu_read_unlock();
>                  return ret;
>              }
>  
> @@ -2672,6 +2684,7 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
>          }
>      }
>  
> +    rcu_read_unlock();
>      return done;
>  }
>  
> @@ -2705,12 +2718,20 @@ static ssize_t qio_channel_rdma_readv(QIOChannel *ioc,
>                                        Error **errp)
>  {
>      QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(ioc);
> -    RDMAContext *rdma = rioc->rdma;
> +    RDMAContext *rdma;
>      RDMAControlHeader head;
>      int ret = 0;
>      ssize_t i;
>      size_t done = 0;
>  
> +    rcu_read_lock();
> +    rdma = atomic_rcu_read(&rioc->rdmain);
> +
> +    if (!rdma) {
> +        rcu_read_unlock();
> +        return -EIO;
> +    }
> +
>      CHECK_ERROR_STATE();
>  
>      for (i = 0; i < niov; i++) {
> @@ -2722,7 +2743,7 @@ static ssize_t qio_channel_rdma_readv(QIOChannel *ioc,
>           * were given and dish out the bytes until we run
>           * out of bytes.
>           */
> -        ret = qemu_rdma_fill(rioc->rdma, data, want, 0);
> +        ret = qemu_rdma_fill(rdma, data, want, 0);
>          done += ret;
>          want -= ret;
>          /* Got what we needed, so go to next iovec */
> @@ -2744,25 +2765,28 @@ static ssize_t qio_channel_rdma_readv(QIOChannel *ioc,
>  
>          if (ret < 0) {
>              rdma->error_state = ret;
> +            rcu_read_unlock();
>              return ret;
>          }
>  
>          /*
>           * SEND was received with new bytes, now try again.
>           */
> -        ret = qemu_rdma_fill(rioc->rdma, data, want, 0);
> +        ret = qemu_rdma_fill(rdma, data, want, 0);
>          done += ret;
>          want -= ret;
>  
>          /* Still didn't get enough, so lets just return */
>          if (want) {
>              if (done == 0) {
> +                rcu_read_unlock();
>                  return QIO_CHANNEL_ERR_BLOCK;
>              } else {
>                  break;
>              }
>          }
>      }
> +    rcu_read_unlock();
>      return done;
>  }
>  
> @@ -2814,15 +2838,29 @@ qio_channel_rdma_source_prepare(GSource *source,
>                                  gint *timeout)
>  {
>      QIOChannelRDMASource *rsource = (QIOChannelRDMASource *)source;
> -    RDMAContext *rdma = rsource->rioc->rdma;
> +    RDMAContext *rdma;
>      GIOCondition cond = 0;
>      *timeout = -1;
>  
> +    rcu_read_lock();
> +    if (rsource->condition == G_IO_IN) {
> +        rdma = atomic_rcu_read(&rsource->rioc->rdmain);
> +    } else {
> +        rdma = atomic_rcu_read(&rsource->rioc->rdmaout);
> +    }
> +
> +    if (!rdma) {
> +        error_report("RDMAContext is NULL when prepare Gsource");
> +        rcu_read_unlock();
> +        return FALSE;
> +    }
> +
>      if (rdma->wr_data[0].control_len) {
>          cond |= G_IO_IN;
>      }
>      cond |= G_IO_OUT;
>  
> +    rcu_read_unlock();
>      return cond & rsource->condition;
>  }
>  
> @@ -2830,14 +2868,28 @@ static gboolean
>  qio_channel_rdma_source_check(GSource *source)
>  {
>      QIOChannelRDMASource *rsource = (QIOChannelRDMASource *)source;
> -    RDMAContext *rdma = rsource->rioc->rdma;
> +    RDMAContext *rdma;
>      GIOCondition cond = 0;
>  
> +    rcu_read_lock();
> +    if (rsource->condition == G_IO_IN) {
> +        rdma = atomic_rcu_read(&rsource->rioc->rdmain);
> +    } else {
> +        rdma = atomic_rcu_read(&rsource->rioc->rdmaout);
> +    }
> +
> +    if (!rdma) {
> +        error_report("RDMAContext is NULL when check Gsource");
> +        rcu_read_unlock();
> +        return FALSE;
> +    }
> +
>      if (rdma->wr_data[0].control_len) {
>          cond |= G_IO_IN;
>      }
>      cond |= G_IO_OUT;
>  
> +    rcu_read_unlock();
>      return cond & rsource->condition;
>  }
>  
> @@ -2848,14 +2900,28 @@ qio_channel_rdma_source_dispatch(GSource *source,
>  {
>      QIOChannelFunc func = (QIOChannelFunc)callback;
>      QIOChannelRDMASource *rsource = (QIOChannelRDMASource *)source;
> -    RDMAContext *rdma = rsource->rioc->rdma;
> +    RDMAContext *rdma;
>      GIOCondition cond = 0;
>  
> +    rcu_read_lock();
> +    if (rsource->condition == G_IO_IN) {
> +        rdma = atomic_rcu_read(&rsource->rioc->rdmain);
> +    } else {
> +        rdma = atomic_rcu_read(&rsource->rioc->rdmaout);
> +    }
> +
> +    if (!rdma) {
> +        error_report("RDMAContext is NULL when dispatch Gsource");
> +        rcu_read_unlock();
> +        return FALSE;
> +    }
> +
>      if (rdma->wr_data[0].control_len) {
>          cond |= G_IO_IN;
>      }
>      cond |= G_IO_OUT;
>  
> +    rcu_read_unlock();
>      return (*func)(QIO_CHANNEL(rsource->rioc),
>                     (cond & rsource->condition),
>                     user_data);
> @@ -2900,15 +2966,32 @@ static int qio_channel_rdma_close(QIOChannel *ioc,
>                                    Error **errp)
>  {
>      QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(ioc);
> +    RDMAContext *rdmain, *rdmaout;
>      trace_qemu_rdma_close();
> -    if (rioc->rdma) {
> -        if (!rioc->rdma->error_state) {
> -            rioc->rdma->error_state = qemu_file_get_error(rioc->file);
> -        }
> -        qemu_rdma_cleanup(rioc->rdma);
> -        g_free(rioc->rdma);
> -        rioc->rdma = NULL;
> +
> +    rdmain = rioc->rdmain;
> +    if (rdmain) {
> +        atomic_rcu_set(&rioc->rdmain, NULL);
> +    }
> +
> +    rdmaout = rioc->rdmaout;
> +    if (rdmaout) {
> +        atomic_rcu_set(&rioc->rdmaout, NULL);
>      }
> +
> +    synchronize_rcu();
> +
> +    if (rdmain) {
> +        qemu_rdma_cleanup(rdmain);
> +    }
> +
> +    if (rdmaout) {
> +        qemu_rdma_cleanup(rdmaout);
> +    }
> +
> +    g_free(rdmain);
> +    g_free(rdmaout);
> +
>      return 0;
>  }
>  
> @@ -2951,12 +3034,21 @@ static size_t qemu_rdma_save_page(QEMUFile *f, void 
> *opaque,
>                                    size_t size, uint64_t *bytes_sent)
>  {
>      QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(opaque);
> -    RDMAContext *rdma = rioc->rdma;
> +    RDMAContext *rdma;
>      int ret;
>  
> +    rcu_read_lock();
> +    rdma = atomic_rcu_read(&rioc->rdmaout);
> +
> +    if (!rdma) {
> +        rcu_read_unlock();
> +        return -EIO;
> +    }
> +
>      CHECK_ERROR_STATE();
>  
>      if (migrate_get_current()->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) {
> +        rcu_read_unlock();
>          return RAM_SAVE_CONTROL_NOT_SUPP;
>      }
>  
> @@ -3041,9 +3133,11 @@ static size_t qemu_rdma_save_page(QEMUFile *f, void 
> *opaque,
>          }
>      }
>  
> +    rcu_read_unlock();
>      return RAM_SAVE_CONTROL_DELAYED;
>  err:
>      rdma->error_state = ret;
> +    rcu_read_unlock();
>      return ret;
>  }
>  
> @@ -3219,8 +3313,8 @@ static int qemu_rdma_registration_handle(QEMUFile *f, 
> void *opaque)
>      RDMAControlHeader blocks = { .type = RDMA_CONTROL_RAM_BLOCKS_RESULT,
>                                   .repeat = 1 };
>      QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(opaque);
> -    RDMAContext *rdma = rioc->rdma;
> -    RDMALocalBlocks *local = &rdma->local_ram_blocks;
> +    RDMAContext *rdma;
> +    RDMALocalBlocks *local;
>      RDMAControlHeader head;
>      RDMARegister *reg, *registers;
>      RDMACompress *comp;
> @@ -3233,8 +3327,17 @@ static int qemu_rdma_registration_handle(QEMUFile *f, 
> void *opaque)
>      int count = 0;
>      int i = 0;
>  
> +    rcu_read_lock();
> +    rdma = atomic_rcu_read(&rioc->rdmain);
> +
> +    if (!rdma) {
> +        rcu_read_unlock();
> +        return -EIO;
> +    }
> +
>      CHECK_ERROR_STATE();
>  
> +    local = &rdma->local_ram_blocks;
>      do {
>          trace_qemu_rdma_registration_handle_wait();
>  
> @@ -3468,6 +3571,7 @@ out:
>      if (ret < 0) {
>          rdma->error_state = ret;
>      }
> +    rcu_read_unlock();
>      return ret;
>  }
>  
> @@ -3481,10 +3585,18 @@ out:
>  static int
>  rdma_block_notification_handle(QIOChannelRDMA *rioc, const char *name)
>  {
> -    RDMAContext *rdma = rioc->rdma;
> +    RDMAContext *rdma;
>      int curr;
>      int found = -1;
>  
> +    rcu_read_lock();
> +    rdma = atomic_rcu_read(&rioc->rdmain);
> +
> +    if (!rdma) {
> +        rcu_read_unlock();
> +        return -EIO;
> +    }
> +
>      /* Find the matching RAMBlock in our local list */
>      for (curr = 0; curr < rdma->local_ram_blocks.nb_blocks; curr++) {
>          if (!strcmp(rdma->local_ram_blocks.block[curr].block_name, name)) {
> @@ -3495,6 +3607,7 @@ rdma_block_notification_handle(QIOChannelRDMA *rioc, 
> const char *name)
>  
>      if (found == -1) {
>          error_report("RAMBlock '%s' not found on destination", name);
> +        rcu_read_unlock();
>          return -ENOENT;
>      }
>  
> @@ -3502,6 +3615,7 @@ rdma_block_notification_handle(QIOChannelRDMA *rioc, 
> const char *name)
>      trace_rdma_block_notification_handle(name, rdma->next_src_index);
>      rdma->next_src_index++;
>  
> +    rcu_read_unlock();
>      return 0;
>  }
>  
> @@ -3524,11 +3638,19 @@ static int qemu_rdma_registration_start(QEMUFile *f, 
> void *opaque,
>                                          uint64_t flags, void *data)
>  {
>      QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(opaque);
> -    RDMAContext *rdma = rioc->rdma;
> +    RDMAContext *rdma;
> +
> +    rcu_read_lock();
> +    rdma = atomic_rcu_read(&rioc->rdmaout);
> +    if (!rdma) {
> +        rcu_read_unlock();
> +        return -EIO;
> +    }
>  
>      CHECK_ERROR_STATE();
>  
>      if (migrate_get_current()->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) {
> +        rcu_read_unlock();
>          return 0;
>      }
>  
> @@ -3536,6 +3658,7 @@ static int qemu_rdma_registration_start(QEMUFile *f, 
> void *opaque,
>      qemu_put_be64(f, RAM_SAVE_FLAG_HOOK);
>      qemu_fflush(f);
>  
> +    rcu_read_unlock();
>      return 0;
>  }
>  
> @@ -3548,13 +3671,21 @@ static int qemu_rdma_registration_stop(QEMUFile *f, 
> void *opaque,
>  {
>      Error *local_err = NULL, **errp = &local_err;
>      QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(opaque);
> -    RDMAContext *rdma = rioc->rdma;
> +    RDMAContext *rdma;
>      RDMAControlHeader head = { .len = 0, .repeat = 1 };
>      int ret = 0;
>  
> +    rcu_read_lock();
> +    rdma = atomic_rcu_read(&rioc->rdmaout);
> +    if (!rdma) {
> +        rcu_read_unlock();
> +        return -EIO;
> +    }
> +
>      CHECK_ERROR_STATE();
>  
>      if (migrate_get_current()->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) {
> +        rcu_read_unlock();
>          return 0;
>      }
>  
> @@ -3586,6 +3717,7 @@ static int qemu_rdma_registration_stop(QEMUFile *f, 
> void *opaque,
>                      qemu_rdma_reg_whole_ram_blocks : NULL);
>          if (ret < 0) {
>              ERROR(errp, "receiving remote info!");
> +            rcu_read_unlock();
>              return ret;
>          }
>  
> @@ -3609,6 +3741,7 @@ static int qemu_rdma_registration_stop(QEMUFile *f, 
> void *opaque,
>                          "not identical on both the source and destination.",
>                          local->nb_blocks, nb_dest_blocks);
>              rdma->error_state = -EINVAL;
> +            rcu_read_unlock();
>              return -EINVAL;
>          }
>  
> @@ -3625,6 +3758,7 @@ static int qemu_rdma_registration_stop(QEMUFile *f, 
> void *opaque,
>                              local->block[i].length,
>                              rdma->dest_blocks[i].length);
>                  rdma->error_state = -EINVAL;
> +                rcu_read_unlock();
>                  return -EINVAL;
>              }
>              local->block[i].remote_host_addr =
> @@ -3642,9 +3776,11 @@ static int qemu_rdma_registration_stop(QEMUFile *f, 
> void *opaque,
>          goto err;
>      }
>  
> +    rcu_read_unlock();
>      return 0;
>  err:
>      rdma->error_state = ret;
> +    rcu_read_unlock();
>      return ret;
>  }
>  
> @@ -3662,10 +3798,15 @@ static const QEMUFileHooks rdma_write_hooks = {
>  static void qio_channel_rdma_finalize(Object *obj)
>  {
>      QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(obj);
> -    if (rioc->rdma) {
> -        qemu_rdma_cleanup(rioc->rdma);
> -        g_free(rioc->rdma);
> -        rioc->rdma = NULL;
> +    if (rioc->rdmain) {
> +        qemu_rdma_cleanup(rioc->rdmain);
> +        g_free(rioc->rdmain);
> +        rioc->rdmain = NULL;
> +    }
> +    if (rioc->rdmaout) {
> +        qemu_rdma_cleanup(rioc->rdmaout);
> +        g_free(rioc->rdmaout);
> +        rioc->rdmaout = NULL;
>      }
>  }
>  
> @@ -3705,13 +3846,16 @@ static QEMUFile *qemu_fopen_rdma(RDMAContext *rdma, 
> const char *mode)
>      }
>  
>      rioc = QIO_CHANNEL_RDMA(object_new(TYPE_QIO_CHANNEL_RDMA));
> -    rioc->rdma = rdma;
>  
>      if (mode[0] == 'w') {
>          rioc->file = qemu_fopen_channel_output(QIO_CHANNEL(rioc));
> +        rioc->rdmaout = rdma;
> +        rioc->rdmain = rdma->return_path;
>          qemu_file_set_hooks(rioc->file, &rdma_write_hooks);
>      } else {
>          rioc->file = qemu_fopen_channel_input(QIO_CHANNEL(rioc));
> +        rioc->rdmain = rdma;
> +        rioc->rdmaout = rdma->return_path;
>          qemu_file_set_hooks(rioc->file, &rdma_read_hooks);
>      }
>  
> diff --git a/migration/savevm.c b/migration/savevm.c
> index c2f34ff..21c07d4 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1622,6 +1622,7 @@ static void *postcopy_ram_listen_thread(void *opaque)
>      qemu_sem_post(&mis->listen_thread_sem);
>      trace_postcopy_ram_listen_thread_start();
>  
> +    rcu_register_thread();
>      /*
>       * Because we're a thread and not a coroutine we can't yield
>       * in qemu_file, and thus we must be blocking now.
> @@ -1662,6 +1663,7 @@ static void *postcopy_ram_listen_thread(void *opaque)
>           * to leave the guest running and fire MCEs for pages that never
>           * arrived as a desperate recovery step.
>           */
> +        rcu_unregister_thread();
>          exit(EXIT_FAILURE);
>      }
>  
> @@ -1676,6 +1678,7 @@ static void *postcopy_ram_listen_thread(void *opaque)
>      migration_incoming_state_destroy();
>      qemu_loadvm_state_cleanup();
>  
> +    rcu_unregister_thread();
>      return NULL;
>  }
>  
> -- 
> 1.8.3.1
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK