RE: [PATCH v3 3/6] net/colo-compare.c: Fix deadlock in compare_chr_send

["Zhang, Chen" <chen.zhang@intel.com>]

> -----Original Message-----
> From: Lukas Straub <lukasstraub2@web.de>
> Sent: Monday, April 27, 2020 5:19 AM
> To: qemu-devel <qemu-devel@nongnu.org>
> Cc: Zhang, Chen <chen.zhang@intel.com>; Li Zhijian
> <lizhijian@cn.fujitsu.com>; Jason Wang <jasowang@redhat.com>; Marc-
> André Lureau <marcandre.lureau@redhat.com>; Paolo Bonzini
> <pbonzini@redhat.com>
> Subject: [PATCH v3 3/6] net/colo-compare.c: Fix deadlock in
> compare_chr_send
> 
> The chr_out chardev is connected to a filter-redirector running in the main
> loop. qemu_chr_fe_write_all might block here in compare_chr_send if the
> (socket-)buffer is full.
> If another filter-redirector in the main loop want's to send data to chr_pri_in
> it might also block if the buffer is full. This leads to a deadlock because both
> event loops get blocked.
> 
> Fix this by converting compare_chr_send to a coroutine and putting the
> packets in a send queue. Also create a new function notify_chr_send, since
> that should be independend.
> 
> Signed-off-by: Lukas Straub <lukasstraub2@web.de>
> ---
>  net/colo-compare.c | 173 ++++++++++++++++++++++++++++++++++-------
> ----
>  1 file changed, 130 insertions(+), 43 deletions(-)
> 
> diff --git a/net/colo-compare.c b/net/colo-compare.c index
> 1de4220fe2..ff6a740284 100644
> --- a/net/colo-compare.c
> +++ b/net/colo-compare.c
> @@ -32,6 +32,9 @@
>  #include "migration/migration.h"
>  #include "util.h"
> 
> +#include "block/aio-wait.h"
> +#include "qemu/coroutine.h"
> +
>  #define TYPE_COLO_COMPARE "colo-compare"
>  #define COLO_COMPARE(obj) \
>      OBJECT_CHECK(CompareState, (obj), TYPE_COLO_COMPARE) @@ -77,6
> +80,20 @@ static int event_unhandled_count;
>   *                    |packet  |  |packet  +    |packet  | |packet  +
>   *                    +--------+  +--------+    +--------+ +--------+
>   */
> +
> +typedef struct SendCo {
> +    Coroutine *co;
> +    GQueue send_list;
> +    bool done;
> +    int ret;
> +} SendCo;
> +
> +typedef struct SendEntry {
> +    uint32_t size;
> +    uint32_t vnet_hdr_len;
> +    uint8_t buf[];
> +} SendEntry;
> +
>  typedef struct CompareState {
>      Object parent;
> 
> @@ -91,6 +108,7 @@ typedef struct CompareState {
>      SocketReadState pri_rs;
>      SocketReadState sec_rs;
>      SocketReadState notify_rs;
> +    SendCo sendco;
>      bool vnet_hdr;
>      uint32_t compare_timeout;
>      uint32_t expired_scan_cycle;
> @@ -126,8 +144,11 @@ enum {
>  static int compare_chr_send(CompareState *s,
>                              const uint8_t *buf,
>                              uint32_t size,
> -                            uint32_t vnet_hdr_len,
> -                            bool notify_remote_frame);
> +                            uint32_t vnet_hdr_len);
> +
> +static int notify_chr_send(CompareState *s,
> +                           const uint8_t *buf,
> +                           uint32_t size);
> 
>  static bool packet_matches_str(const char *str,
>                                 const uint8_t *buf, @@ -145,7 +166,7 @@ static void
> notify_remote_frame(CompareState *s)
>      char msg[] = "DO_CHECKPOINT";
>      int ret = 0;
> 
> -    ret = compare_chr_send(s, (uint8_t *)msg, strlen(msg), 0, true);
> +    ret = notify_chr_send(s, (uint8_t *)msg, strlen(msg));
>      if (ret < 0) {
>          error_report("Notify Xen COLO-frame failed");
>      }
> @@ -271,8 +292,7 @@ static void colo_release_primary_pkt(CompareState
> *s, Packet *pkt)
>      ret = compare_chr_send(s,
>                             pkt->data,
>                             pkt->size,
> -                           pkt->vnet_hdr_len,
> -                           false);
> +                           pkt->vnet_hdr_len);
>      if (ret < 0) {
>          error_report("colo send primary packet failed");
>      }
> @@ -699,63 +719,123 @@ static void colo_compare_connection(void
> *opaque, void *user_data)
>      }
>  }
> 
> -static int compare_chr_send(CompareState *s,
> -                            const uint8_t *buf,
> -                            uint32_t size,
> -                            uint32_t vnet_hdr_len,
> -                            bool notify_remote_frame)
> +static void coroutine_fn _compare_chr_send(void *opaque)
>  {
> +    CompareState *s = opaque;
> +    SendCo *sendco = &s->sendco;
>      int ret = 0;
> -    uint32_t len = htonl(size);
> 
> -    if (!size) {
> -        return 0;
> -    }
> +    while (!g_queue_is_empty(&sendco->send_list)) {
> +        SendEntry *entry = g_queue_pop_tail(&sendco->send_list);
> +        uint32_t len = htonl(entry->size);
> 
> -    if (notify_remote_frame) {
> -        ret = qemu_chr_fe_write_all(&s->chr_notify_dev,
> -                                    (uint8_t *)&len,
> -                                    sizeof(len));
> -    } else {
>          ret = qemu_chr_fe_write_all(&s->chr_out, (uint8_t *)&len, sizeof(len));
> -    }
> 
> -    if (ret != sizeof(len)) {
> -        goto err;
> -    }
> +        if (ret != sizeof(len)) {
> +            g_free(entry);
> +            goto err;
> +        }
> 
> -    if (s->vnet_hdr) {
> -        /*
> -         * We send vnet header len make other module(like filter-redirector)
> -         * know how to parse net packet correctly.
> -         */
> -        len = htonl(vnet_hdr_len);
> +        if (s->vnet_hdr) {
> +            /*
> +             * We send vnet header len make other module(like filter-redirector)
> +             * know how to parse net packet correctly.
> +             */
> +            len = htonl(entry->vnet_hdr_len);
> 
> -        if (!notify_remote_frame) {
>              ret = qemu_chr_fe_write_all(&s->chr_out,
>                                          (uint8_t *)&len,
>                                          sizeof(len));
> +
> +            if (ret != sizeof(len)) {
> +                g_free(entry);
> +                goto err;
> +            }
>          }
> 
> -        if (ret != sizeof(len)) {
> +        ret = qemu_chr_fe_write_all(&s->chr_out,
> +                                    (uint8_t *)entry->buf,
> +                                    entry->size);
> +
> +        if (ret != entry->size) {
> +            g_free(entry);
>              goto err;
>          }
> +
> +        g_free(entry);
>      }
> 
> -    if (notify_remote_frame) {
> -        ret = qemu_chr_fe_write_all(&s->chr_notify_dev,
> -                                    (uint8_t *)buf,
> -                                    size);
> -    } else {
> -        ret = qemu_chr_fe_write_all(&s->chr_out, (uint8_t *)buf, size);
> +    sendco->ret = 0;
> +    goto out;
> +
> +err:
> +    while (!g_queue_is_empty(&sendco->send_list)) {
> +        SendEntry *entry = g_queue_pop_tail(&sendco->send_list);
> +        g_free(entry);
>      }
> +    sendco->ret = ret < 0 ? ret : -EIO;
> +out:
> +    sendco->co = NULL;
> +    sendco->done = true;
> +    aio_wait_kick();
> +}
> +
> +static int compare_chr_send(CompareState *s,
> +                            const uint8_t *buf,
> +                            uint32_t size,
> +                            uint32_t vnet_hdr_len) {
> +    SendCo *sendco = &s->sendco;
> +    SendEntry *entry;
> +
> +    if (!size) {
> +        return 0;
> +    }
> +
> +    entry = g_malloc(sizeof(SendEntry) + size);
> +    entry->size = size;
> +    entry->vnet_hdr_len = vnet_hdr_len;
> +    memcpy(entry->buf, buf, size);
> +    g_queue_push_head(&sendco->send_list, entry);
> +
> +    if (sendco->done) {
> +        sendco->co = qemu_coroutine_create(_compare_chr_send, s);
> +        sendco->done = false;
> +        qemu_coroutine_enter(sendco->co);
> +        if (sendco->done) {
> +            /* report early errors */
> +            return sendco->ret;
> +        }
> +    }
> +
> +    /* assume success */
> +    return 0;
> +}
> +

Why not make notify_chr_send same as compare_chr_send?

Thanks
Zhang Chen

> +static int notify_chr_send(CompareState *s,
> +                           const uint8_t *buf,
> +                           uint32_t size) {
> +    int ret = 0;
> +    uint32_t len = htonl(size);
> +
> +    ret = qemu_chr_fe_write_all(&s->chr_notify_dev,
> +                            (uint8_t *)&len,
> +                            sizeof(len));
> +
> +    if (ret != sizeof(len)) {
> +        goto err;
> +    }
> +
> +    ret = qemu_chr_fe_write_all(&s->chr_notify_dev,
> +                                (uint8_t *)buf,
> +                                size);
> 
>      if (ret != size) {
>          goto err;
>      }
> 
>      return 0;
> -
>  err:
>      return ret < 0 ? ret : -EIO;
>  }
> @@ -1062,8 +1142,7 @@ static void
> compare_pri_rs_finalize(SocketReadState *pri_rs)
>          compare_chr_send(s,
>                           pri_rs->buf,
>                           pri_rs->packet_len,
> -                         pri_rs->vnet_hdr_len,
> -                         false);
> +                         pri_rs->vnet_hdr_len);
>      } else {
>          /* compare packet in the specified connection */
>          colo_compare_connection(conn, s); @@ -1093,7 +1172,7 @@ static void
> compare_notify_rs_finalize(SocketReadState *notify_rs)
>      if (packet_matches_str("COLO_USERSPACE_PROXY_INIT",
>                             notify_rs->buf,
>                             notify_rs->packet_len)) {
> -        ret = compare_chr_send(s, (uint8_t *)msg, strlen(msg), 0, true);
> +        ret = notify_chr_send(s, (uint8_t *)msg, strlen(msg));
>          if (ret < 0) {
>              error_report("Notify Xen COLO-frame INIT failed");
>          }
> @@ -1199,6 +1278,9 @@ static void colo_compare_complete(UserCreatable
> *uc, Error **errp)
> 
>      QTAILQ_INSERT_TAIL(&net_compares, s, next);
> 
> +    s->sendco.done = true;
> +    g_queue_init(&s->sendco.send_list);
> +
>      g_queue_init(&s->conn_list);
> 
>      qemu_mutex_init(&event_mtx);
> @@ -1224,8 +1306,7 @@ static void colo_flush_packets(void *opaque, void
> *user_data)
>          compare_chr_send(s,
>                           pkt->data,
>                           pkt->size,
> -                         pkt->vnet_hdr_len,
> -                         false);
> +                         pkt->vnet_hdr_len);
>          packet_destroy(pkt, NULL);
>      }
>      while (!g_queue_is_empty(&conn->secondary_list)) { @@ -1281,6
> +1362,11 @@ static void colo_compare_finalize(Object *obj)
>      CompareState *s = COLO_COMPARE(obj);
>      CompareState *tmp = NULL;
> 
> +    AioContext *ctx = iothread_get_aio_context(s->iothread);
> +    aio_context_acquire(ctx);
> +    AIO_WAIT_WHILE(ctx, !s->sendco.done);
> +    aio_context_release(ctx);
> +
>      qemu_chr_fe_deinit(&s->chr_pri_in, false);
>      qemu_chr_fe_deinit(&s->chr_sec_in, false);
>      qemu_chr_fe_deinit(&s->chr_out, false); @@ -1305,6 +1391,7 @@ static
> void colo_compare_finalize(Object *obj)
>      g_queue_foreach(&s->conn_list, colo_flush_packets, s);
> 
>      g_queue_clear(&s->conn_list);
> +    g_queue_clear(&s->sendco.send_list);
> 
>      if (s->connection_track_table) {
>          g_hash_table_destroy(s->connection_track_table);
> --
> 2.20.1