Do not duplicate blockstore operations when io_uring fills up

This bug was leading to OSDs dying with "Assertion `fulfilled == read_op->len' failed"
when testing fio -rw=randread -numjobs=8 -iodepth=128

src/blockstore_impl.cpp

@@ -105,10 +105,10 @@ void blockstore_impl_t::loop()
         // has_writes == 1 - some writes in progress
         // has_writes == 2 - tried to submit some writes, but failed
         int has_writes = 0, op_idx = 0, new_idx = 0;
-        for (; op_idx < submit_queue.size(); op_idx++)
+        for (; op_idx < submit_queue.size(); op_idx++, new_idx++)
         {
             auto op = submit_queue[op_idx];
-            submit_queue[new_idx++] = op;
+            submit_queue[new_idx] = op;
             // FIXME: This needs some simplification
             // Writes should not block reads if the ring is not full and reads don't depend on them
             // In all other cases we should stop submission

src/blockstore_read.cpp

@@ -191,8 +191,8 @@ int blockstore_impl_t::dequeue_read(blockstore_op_t *read_op)
                     if (bmp_end > bmp_start)
                     {
                         // fill with zeroes
-                        fulfill_read(read_op, fulfilled, bmp_start * bitmap_granularity,
-                            bmp_end * bitmap_granularity, (BS_ST_DELETE | BS_ST_STABLE), 0, 0);
+                        assert(fulfill_read(read_op, fulfilled, bmp_start * bitmap_granularity,
+                            bmp_end * bitmap_granularity, (BS_ST_DELETE | BS_ST_STABLE), 0, 0));
                     }
                     bmp_start = bmp_end;
                     while (clean_entry_bitmap[bmp_end >> 3] & (1 << (bmp_end & 0x7)) && bmp_end < bmp_size)
@@ -218,7 +218,7 @@ int blockstore_impl_t::dequeue_read(blockstore_op_t *read_op)
     else if (fulfilled < read_op->len)
     {
         // fill remaining parts with zeroes
-        fulfill_read(read_op, fulfilled, 0, block_size, (BS_ST_DELETE | BS_ST_STABLE), 0, 0);
+        assert(fulfill_read(read_op, fulfilled, 0, block_size, (BS_ST_DELETE | BS_ST_STABLE), 0, 0));
     }
     assert(fulfilled == read_op->len);
     read_op->version = result_version;