Fix WAITAOF mix-use last_offset and last_numreplicas (#11922)

There be a situation that satisfies WAIT, and then wrongly unblock
WAITAOF because we mix-use last_offset and last_numreplicas.

We update last_offset and last_numreplicas only when the condition
matches. i.e. output of either replicationCountAOFAcksByOffset or
replicationCountAcksByOffset is right.

In this case, we need to have separate last_ variables for each of
them. Added a last_aof_offset and last_aof_numreplicas for WAITAOF.

WAITAOF was added in #11713. Found while coding #11917.
A Test was added to validate that case.

src/replication.c

@@ -3612,7 +3612,9 @@ void unblockClientWaitingReplicas(client *c) {
  * since we received enough ACKs from slaves. */
 void processClientsWaitingReplicas(void) {
     long long last_offset = 0;
+    long long last_aof_offset = 0;
     int last_numreplicas = 0;
+    int last_aof_numreplicas = 0;
 
     listIter li;
     listNode *ln;
@@ -3628,7 +3630,7 @@ void processClientsWaitingReplicas(void) {
         if (is_wait_aof && c->bstate.numlocal && !server.aof_enabled) {
             addReplyError(c, "WAITAOF cannot be used when numlocal is set but appendonly is disabled.");
             unblockClient(c);
-            return;
+            continue;
         }
 
         /* Every time we find a client that is satisfied for a given
@@ -3636,10 +3638,14 @@ void processClientsWaitingReplicas(void) {
          * may be unblocked without calling replicationCountAcksByOffset()
          * or calling replicationCountAOFAcksByOffset()
          * if the requested offset / replicas were equal or less. */
-        if (last_offset && last_offset >= c->bstate.reploffset &&
+        if (!is_wait_aof && last_offset && last_offset >= c->bstate.reploffset &&
                            last_numreplicas >= c->bstate.numreplicas)
         {
             numreplicas = last_numreplicas;
+        } else if (is_wait_aof && last_aof_offset && last_aof_offset >= c->bstate.reploffset &&
+                    last_aof_numreplicas >= c->bstate.numreplicas)
+        {
+            numreplicas = last_aof_numreplicas;
         } else {
             numreplicas = is_wait_aof ?
                 replicationCountAOFAcksByOffset(c->bstate.reploffset) :
@@ -3648,8 +3654,13 @@ void processClientsWaitingReplicas(void) {
             /* Check if the number of replicas is satisfied. */
             if (numreplicas < c->bstate.numreplicas) continue;
 
-            last_offset = c->bstate.reploffset;
-            last_numreplicas = numreplicas;
+            if (is_wait_aof) {
+                last_aof_offset = c->bstate.reploffset;
+                last_aof_numreplicas = numreplicas;
+            } else {
+                last_offset = c->bstate.reploffset;
+                last_numreplicas = numreplicas;
+            }
         }
 
         /* Check if the local constraint of WAITAOF is served */

src/server.h

@@ -1009,7 +1009,7 @@ typedef struct blockingState {
     /* BLOCKED_LIST, BLOCKED_ZSET and BLOCKED_STREAM or any other Keys related blocking */
     dict *keys;                 /* The keys we are blocked on */
 
-    /* BLOCKED_WAIT */
+    /* BLOCKED_WAIT and BLOCKED_WAITAOF */
     int numreplicas;        /* Number of replicas we are waiting for ACK. */
     int numlocal;           /* Indication if WAITAOF is waiting for local fsync. */
     long long reploffset;   /* Replication offset to reach. */

tests/unit/wait.tcl

@@ -360,3 +360,73 @@ tags {"wait aof network external:skip"} {
         }
     }
 }
+
+start_server {tags {"failover external:skip"}} {
+start_server {} {
+start_server {} {
+    set master [srv 0 client]
+    set master_host [srv 0 host]
+    set master_port [srv 0 port]
+
+    set replica1 [srv -1 client]
+    set replica1_pid [srv -1 pid]
+
+    set replica2 [srv -2 client]
+
+    test {setup replication for following tests} {
+        $replica1 replicaof $master_host $master_port
+        $replica2 replicaof $master_host $master_port
+        wait_for_sync $replica1
+        wait_for_sync $replica2
+    }
+
+    test {WAIT and WAITAOF replica multiple clients unblock - reuse last result} {
+        set rd [redis_deferring_client]
+        set rd2 [redis_deferring_client]
+
+        $master config set appendonly yes
+        $replica1 config set appendonly yes
+        $replica2 config set appendonly yes
+
+        $master config set appendfsync always
+        $replica1 config set appendfsync no
+        $replica2 config set appendfsync no
+
+        waitForBgrewriteaof $master
+        waitForBgrewriteaof $replica1
+        waitForBgrewriteaof $replica2
+
+        exec kill -SIGSTOP $replica1_pid
+
+        $rd incr foo
+        $rd read
+        $rd waitaof 0 1 0
+
+        # rd2 has a newer repl_offset
+        $rd2 incr foo
+        $rd2 read
+        $rd2 wait 2 0
+
+        wait_for_blocked_clients_count 2
+
+        exec kill -SIGCONT $replica1_pid
+
+        # WAIT will unblock the client first.
+        assert_equal [$rd2 read] {2}
+
+        # Make $replica1 catch up the repl_aof_off, then WAITAOF will unblock the client.
+        $replica1 config set appendfsync always
+        $master incr foo
+        assert_equal [$rd read] {1 1}
+
+        $rd ping
+        assert_equal [$rd read] {PONG}
+        $rd2 ping
+        assert_equal [$rd2 read] {PONG}
+
+        $rd close
+        $rd2 close
+    }
+}
+}
+}