migration: Refactor error handling in source return path

rp_state.error was a boolean used to show error happened in return path
thread.  That's not only duplicating error reporting (migrate_set_error),
but also not good enough in that we only do error_report() and set it to
true, we never can keep a history of the exact error and show it in
query-migrate.

To make this better, a few things done:

  - Use error_setg() rather than error_report() across the whole lifecycle
    of return path thread, keeping the error in an Error*.

  - With above, no need to have mark_source_rp_bad(), remove it, alongside
    with rp_state.error itself.

  - Use migrate_set_error() to apply that captured error to the global
    migration object when error occured in this thread.

  - Do the same when detected qemufile error in source return path

We need to re-export qemu_file_get_error_obj() to do the last one.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20231017202633.296756-2-peterx@redhat.com>

migration/migration.c

@@ -99,7 +99,7 @@ static int migration_maybe_pause(MigrationState *s,
                                  int *current_active_state,
                                  int new_state);
 static void migrate_fd_cancel(MigrationState *s);
-static int close_return_path_on_source(MigrationState *s);
+static bool close_return_path_on_source(MigrationState *s);
 
 static void migration_downtime_start(MigrationState *s)
 {
@@ -1475,7 +1475,6 @@ int migrate_init(MigrationState *s, Error **errp)
     s->to_dst_file = NULL;
     s->state = MIGRATION_STATUS_NONE;
     s->rp_state.from_dst_file = NULL;
-    s->rp_state.error = false;
     s->mbps = 0.0;
     s->pages_per_second = 0.0;
     s->downtime = 0;
@@ -1883,16 +1882,6 @@ void qmp_migrate_continue(MigrationStatus state, Error **errp)
     qemu_sem_post(&s->pause_sem);
 }
 
-/* migration thread support */
-/*
- * Something bad happened to the RP stream, mark an error
- * The caller shall print or trace something to indicate why
- */
-static void mark_source_rp_bad(MigrationState *s)
-{
-    s->rp_state.error = true;
-}
-
 void migration_rp_wait(MigrationState *s)
 {
     qemu_sem_wait(&s->rp_state.rp_sem);
@@ -1923,8 +1912,9 @@ static struct rp_cmd_args {
  * We're allowed to send more than requested (e.g. to round to our page size)
  * and we don't need to send pages that have already been sent.
  */
-static void migrate_handle_rp_req_pages(MigrationState *ms, const char* rbname,
-                                       ram_addr_t start, size_t len)
+static void
+migrate_handle_rp_req_pages(MigrationState *ms, const char* rbname,
+                            ram_addr_t start, size_t len, Error **errp)
 {
     long our_host_ps = qemu_real_host_page_size();
 
@@ -1936,37 +1926,36 @@ static void migrate_handle_rp_req_pages(MigrationState *ms, const char* rbname,
      */
     if (!QEMU_IS_ALIGNED(start, our_host_ps) ||
         !QEMU_IS_ALIGNED(len, our_host_ps)) {
-        error_report("%s: Misaligned page request, start: " RAM_ADDR_FMT
-                     " len: %zd", __func__, start, len);
-        mark_source_rp_bad(ms);
+        error_setg(errp, "MIG_RP_MSG_REQ_PAGES: Misaligned page request, start:"
+                   RAM_ADDR_FMT " len: %zd", start, len);
         return;
     }
 
-    if (ram_save_queue_pages(rbname, start, len)) {
-        mark_source_rp_bad(ms);
-    }
+    ram_save_queue_pages(rbname, start, len, errp);
 }
 
-static int migrate_handle_rp_recv_bitmap(MigrationState *s, char *block_name)
+static int migrate_handle_rp_recv_bitmap(MigrationState *s, char *block_name,
+                                         Error **errp)
 {
     RAMBlock *block = qemu_ram_block_by_name(block_name);
 
     if (!block) {
-        error_report("%s: invalid block name '%s'", __func__, block_name);
+        error_setg(errp, "MIG_RP_MSG_RECV_BITMAP has invalid block name '%s'",
+                   block_name);
         return -EINVAL;
     }
 
     /* Fetch the received bitmap and refresh the dirty bitmap */
-    return ram_dirty_bitmap_reload(s, block);
+    return ram_dirty_bitmap_reload(s, block, errp);
 }
 
-static int migrate_handle_rp_resume_ack(MigrationState *s, uint32_t value)
+static int migrate_handle_rp_resume_ack(MigrationState *s,
+                                        uint32_t value, Error **errp)
 {
     trace_source_return_path_thread_resume_ack(value);
 
     if (value != MIGRATION_RESUME_ACK_VALUE) {
-        error_report("%s: illegal resume_ack value %"PRIu32,
-                     __func__, value);
+        error_setg(errp, "illegal resume_ack value %"PRIu32, value);
         return -1;
     }
 
@@ -2025,48 +2014,46 @@ static void *source_return_path_thread(void *opaque)
     uint32_t tmp32, sibling_error;
     ram_addr_t start = 0; /* =0 to silence warning */
     size_t  len = 0, expected_len;
+    Error *err = NULL;
     int res;
 
     trace_source_return_path_thread_entry();
     rcu_register_thread();
 
-    while (!ms->rp_state.error && !qemu_file_get_error(rp) &&
-           migration_is_setup_or_active(ms->state)) {
+    while (migration_is_setup_or_active(ms->state)) {
         trace_source_return_path_thread_loop_top();
+
         header_type = qemu_get_be16(rp);
         header_len = qemu_get_be16(rp);
 
         if (qemu_file_get_error(rp)) {
-            mark_source_rp_bad(ms);
+            qemu_file_get_error_obj(rp, &err);
             goto out;
         }
 
         if (header_type >= MIG_RP_MSG_MAX ||
             header_type == MIG_RP_MSG_INVALID) {
-            error_report("RP: Received invalid message 0x%04x length 0x%04x",
-                         header_type, header_len);
-            mark_source_rp_bad(ms);
+            error_setg(&err, "Received invalid message 0x%04x length 0x%04x",
+                       header_type, header_len);
             goto out;
         }
 
         if ((rp_cmd_args[header_type].len != -1 &&
             header_len != rp_cmd_args[header_type].len) ||
             header_len > sizeof(buf)) {
-            error_report("RP: Received '%s' message (0x%04x) with"
-                         "incorrect length %d expecting %zu",
-                         rp_cmd_args[header_type].name, header_type, header_len,
-                         (size_t)rp_cmd_args[header_type].len);
-            mark_source_rp_bad(ms);
+            error_setg(&err, "Received '%s' message (0x%04x) with"
+                       "incorrect length %d expecting %zu",
+                       rp_cmd_args[header_type].name, header_type, header_len,
+                       (size_t)rp_cmd_args[header_type].len);
             goto out;
         }
 
         /* We know we've got a valid header by this point */
         res = qemu_get_buffer(rp, buf, header_len);
         if (res != header_len) {
-            error_report("RP: Failed reading data for message 0x%04x"
-                         " read %d expected %d",
-                         header_type, res, header_len);
-            mark_source_rp_bad(ms);
+            error_setg(&err, "Failed reading data for message 0x%04x"
+                       " read %d expected %d",
+                       header_type, res, header_len);
             goto out;
         }
 
@@ -2076,8 +2063,7 @@ static void *source_return_path_thread(void *opaque)
             sibling_error = ldl_be_p(buf);
             trace_source_return_path_thread_shut(sibling_error);
             if (sibling_error) {
-                error_report("RP: Sibling indicated error %d", sibling_error);
-                mark_source_rp_bad(ms);
+                error_setg(&err, "Sibling indicated error %d", sibling_error);
             }
             /*
              * We'll let the main thread deal with closing the RP
@@ -2095,7 +2081,10 @@ static void *source_return_path_thread(void *opaque)
         case MIG_RP_MSG_REQ_PAGES:
             start = ldq_be_p(buf);
             len = ldl_be_p(buf + 8);
-            migrate_handle_rp_req_pages(ms, NULL, start, len);
+            migrate_handle_rp_req_pages(ms, NULL, start, len, &err);
+            if (err) {
+                goto out;
+            }
             break;
 
         case MIG_RP_MSG_REQ_PAGES_ID:
@@ -2110,32 +2099,32 @@ static void *source_return_path_thread(void *opaque)
                 expected_len += tmp32;
             }
             if (header_len != expected_len) {
-                error_report("RP: Req_Page_id with length %d expecting %zd",
-                             header_len, expected_len);
-                mark_source_rp_bad(ms);
+                error_setg(&err, "Req_Page_id with length %d expecting %zd",
+                           header_len, expected_len);
+                goto out;
+            }
+            migrate_handle_rp_req_pages(ms, (char *)&buf[13], start, len,
+                                        &err);
+            if (err) {
                 goto out;
             }
-            migrate_handle_rp_req_pages(ms, (char *)&buf[13], start, len);
             break;
 
         case MIG_RP_MSG_RECV_BITMAP:
             if (header_len < 1) {
-                error_report("%s: missing block name", __func__);
-                mark_source_rp_bad(ms);
+                error_setg(&err, "MIG_RP_MSG_RECV_BITMAP missing block name");
                 goto out;
             }
             /* Format: len (1B) + idstr (<255B). This ends the idstr. */
             buf[buf[0] + 1] = '\0';
-            if (migrate_handle_rp_recv_bitmap(ms, (char *)(buf + 1))) {
-                mark_source_rp_bad(ms);
+            if (migrate_handle_rp_recv_bitmap(ms, (char *)(buf + 1), &err)) {
                 goto out;
             }
             break;
 
         case MIG_RP_MSG_RESUME_ACK:
             tmp32 = ldl_be_p(buf);
-            if (migrate_handle_rp_resume_ack(ms, tmp32)) {
-                mark_source_rp_bad(ms);
+            if (migrate_handle_rp_resume_ack(ms, tmp32, &err)) {
                 goto out;
             }
             break;
@@ -2151,13 +2140,15 @@ static void *source_return_path_thread(void *opaque)
     }
 
 out:
-    if (qemu_file_get_error(rp)) {
+    if (err) {
+        migrate_set_error(ms, err);
+        error_free(err);
         trace_source_return_path_thread_bad_end();
-        mark_source_rp_bad(ms);
     }
 
     trace_source_return_path_thread_end();
     rcu_unregister_thread();
+
     return NULL;
 }
 
@@ -2179,12 +2170,11 @@ static int open_return_path_on_source(MigrationState *ms)
     return 0;
 }
 
-static int close_return_path_on_source(MigrationState *ms)
+/* Return true if error detected, or false otherwise */
+static bool close_return_path_on_source(MigrationState *ms)
 {
-    int ret;
-
     if (!ms->rp_state.rp_thread_created) {
-        return 0;
+        return false;
     }
 
     trace_migration_return_path_end_before();
@@ -2202,18 +2192,13 @@ static int close_return_path_on_source(MigrationState *ms)
         }
     }
 
-    trace_await_return_path_close_on_source_joining();
     qemu_thread_join(&ms->rp_state.rp_thread);
     ms->rp_state.rp_thread_created = false;
-    trace_await_return_path_close_on_source_close();
-
-    ret = ms->rp_state.error;
-    ms->rp_state.error = false;
-
     migration_release_dst_files(ms);
+    trace_migration_return_path_end_after();
 
-    trace_migration_return_path_end_after(ret);
-    return ret;
+    /* Return path will persist the error in MigrationState when quit */
+    return migrate_has_error(ms);
 }
 
 static inline void

migration/migration.h

@@ -308,7 +308,6 @@ struct MigrationState {
         /* Protected by qemu_file_lock */
         QEMUFile     *from_dst_file;
         QemuThread    rp_thread;
-        bool          error;
         /*
          * We can also check non-zero of rp_thread, but there's no "official"
          * way to do this, so this bool makes it slightly more elegant.

migration/qemu-file.c

@@ -137,7 +137,7 @@ QEMUFile *qemu_file_new_input(QIOChannel *ioc)
  *
  * If errp is specified, a verbose error message will be copied over.
  */
-static int qemu_file_get_error_obj(QEMUFile *f, Error **errp)
+int qemu_file_get_error_obj(QEMUFile *f, Error **errp)
 {
     if (!f->last_error) {
         return 0;

migration/qemu-file.h

@@ -68,6 +68,7 @@ int coroutine_mixed_fn qemu_peek_byte(QEMUFile *f, int offset);
 void qemu_file_skip(QEMUFile *f, int size);
 int qemu_file_get_error_obj_any(QEMUFile *f1, QEMUFile *f2, Error **errp);
 void qemu_file_set_error_obj(QEMUFile *f, int ret, Error *err);
+int qemu_file_get_error_obj(QEMUFile *f, Error **errp);
 void qemu_file_set_error(QEMUFile *f, int ret);
 int qemu_file_shutdown(QEMUFile *f);
 QEMUFile *qemu_file_get_return_path(QEMUFile *f);

migration/ram.c

@@ -1898,7 +1898,8 @@ static void migration_page_queue_free(RAMState *rs)
  * @start: starting address from the start of the RAMBlock
  * @len: length (in bytes) to send
  */
-int ram_save_queue_pages(const char *rbname, ram_addr_t start, ram_addr_t len)
+int ram_save_queue_pages(const char *rbname, ram_addr_t start, ram_addr_t len,
+                         Error **errp)
 {
     RAMBlock *ramblock;
     RAMState *rs = ram_state;
@@ -1915,7 +1916,7 @@ int ram_save_queue_pages(const char *rbname, ram_addr_t start, ram_addr_t len)
              * Shouldn't happen, we can't reuse the last RAMBlock if
              * it's the 1st request.
              */
-            error_report("ram_save_queue_pages no previous block");
+            error_setg(errp, "MIG_RP_MSG_REQ_PAGES has no previous block");
             return -1;
         }
     } else {
@@ -1923,16 +1924,17 @@ int ram_save_queue_pages(const char *rbname, ram_addr_t start, ram_addr_t len)
 
         if (!ramblock) {
             /* We shouldn't be asked for a non-existent RAMBlock */
-            error_report("ram_save_queue_pages no block '%s'", rbname);
+            error_setg(errp, "MIG_RP_MSG_REQ_PAGES has no block '%s'", rbname);
             return -1;
         }
         rs->last_req_rb = ramblock;
     }
     trace_ram_save_queue_pages(ramblock->idstr, start, len);
     if (!offset_in_ramblock(ramblock, start + len - 1)) {
-        error_report("%s request overrun start=" RAM_ADDR_FMT " len="
-                     RAM_ADDR_FMT " blocklen=" RAM_ADDR_FMT,
-                     __func__, start, len, ramblock->used_length);
+        error_setg(errp, "MIG_RP_MSG_REQ_PAGES request overrun, "
+                   "start=" RAM_ADDR_FMT " len="
+                   RAM_ADDR_FMT " blocklen=" RAM_ADDR_FMT,
+                   start, len, ramblock->used_length);
         return -1;
     }
 
@@ -1964,9 +1966,9 @@ int ram_save_queue_pages(const char *rbname, ram_addr_t start, ram_addr_t len)
         assert(len % page_size == 0);
         while (len) {
             if (ram_save_host_page_urgent(pss)) {
-                error_report("%s: ram_save_host_page_urgent() failed: "
-                             "ramblock=%s, start_addr=0x"RAM_ADDR_FMT,
-                             __func__, ramblock->idstr, start);
+                error_setg(errp, "ram_save_host_page_urgent() failed: "
+                           "ramblock=%s, start_addr=0x"RAM_ADDR_FMT,
+                           ramblock->idstr, start);
                 ret = -1;
                 break;
             }
@@ -4110,7 +4112,7 @@ static int ram_dirty_bitmap_sync_all(MigrationState *s, RAMState *rs)
  * This is only used when the postcopy migration is paused but wants
  * to resume from a middle point.
  */
-int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *block)
+int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *block, Error **errp)
 {
     int ret = -EINVAL;
     /* from_dst_file is always valid because we're within rp_thread */
@@ -4124,8 +4126,8 @@ int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *block)
     trace_ram_dirty_bitmap_reload_begin(block->idstr);
 
     if (s->state != MIGRATION_STATUS_POSTCOPY_RECOVER) {
-        error_report("%s: incorrect state %s", __func__,
-                     MigrationStatus_str(s->state));
+        error_setg(errp, "Reload bitmap in incorrect state %s",
+                   MigrationStatus_str(s->state));
         return -EINVAL;
     }
 
@@ -4142,9 +4144,8 @@ int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *block)
 
     /* The size of the bitmap should match with our ramblock */
     if (size != local_size) {
-        error_report("%s: ramblock '%s' bitmap size mismatch "
-                     "(0x%"PRIx64" != 0x%"PRIx64")", __func__,
-                     block->idstr, size, local_size);
+        error_setg(errp, "ramblock '%s' bitmap size mismatch (0x%"PRIx64
+                   " != 0x%"PRIx64")", block->idstr, size, local_size);
         return -EINVAL;
     }
 
@@ -4153,15 +4154,15 @@ int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *block)
 
     ret = qemu_file_get_error(file);
     if (ret || size != local_size) {
-        error_report("%s: read bitmap failed for ramblock '%s': %d"
-                     " (size 0x%"PRIx64", got: 0x%"PRIx64")",
-                     __func__, block->idstr, ret, local_size, size);
+        error_setg(errp, "read bitmap failed for ramblock '%s': %d"
+                   " (size 0x%"PRIx64", got: 0x%"PRIx64")",
+                   block->idstr, ret, local_size, size);
         return -EIO;
     }
 
     if (end_mark != RAMBLOCK_RECV_BITMAP_ENDING) {
-        error_report("%s: ramblock '%s' end mark incorrect: 0x%"PRIx64,
-                     __func__, block->idstr, end_mark);
+        error_setg(errp, "ramblock '%s' end mark incorrect: 0x%"PRIx64,
+                   block->idstr, end_mark);
         return -EINVAL;
     }
 

migration/ram.h

@@ -50,7 +50,8 @@ uint64_t ram_bytes_total(void);
 void mig_throttle_counter_reset(void);
 
 uint64_t ram_pagesize_summary(void);
-int ram_save_queue_pages(const char *rbname, ram_addr_t start, ram_addr_t len);
+int ram_save_queue_pages(const char *rbname, ram_addr_t start, ram_addr_t len,
+                         Error **errp);
 void ram_postcopy_migrated_memory_release(MigrationState *ms);
 /* For outgoing discard bitmap */
 void ram_postcopy_send_discard_bitmap(MigrationState *ms);
@@ -70,7 +71,7 @@ void ramblock_recv_bitmap_set(RAMBlock *rb, void *host_addr);
 void ramblock_recv_bitmap_set_range(RAMBlock *rb, void *host_addr, size_t nr);
 int64_t ramblock_recv_bitmap_send(QEMUFile *file,
                                   const char *block_name);
-int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *rb);
+int ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *rb, Error **errp);
 bool ramblock_page_is_discarded(RAMBlock *rb, ram_addr_t start);
 void postcopy_preempt_shutdown_file(MigrationState *s);
 void *postcopy_preempt_thread(void *opaque);

migration/trace-events

@@ -150,8 +150,6 @@ multifd_tls_outgoing_handshake_complete(void *ioc) "ioc=%p"
 multifd_set_outgoing_channel(void *ioc, const char *ioctype, const char *hostname)  "ioc=%p ioctype=%s hostname=%s"
 
 # migration.c
-await_return_path_close_on_source_close(void) ""
-await_return_path_close_on_source_joining(void) ""
 migrate_set_state(const char *new_state) "new state %s"
 migrate_fd_cleanup(void) ""
 migrate_fd_error(const char *error_desc) "error=%s"
@@ -168,7 +166,7 @@ migration_completion_postcopy_end_after_complete(void) ""
 migration_rate_limit_pre(int ms) "%d ms"
 migration_rate_limit_post(int urgent) "urgent: %d"
 migration_return_path_end_before(void) ""
-migration_return_path_end_after(int rp_error) "%d"
+migration_return_path_end_after(void) ""
 migration_thread_after_loop(void) ""
 migration_thread_file_err(void) ""
 migration_thread_setup_complete(void) ""