Fix primary_read bitmap buffers being freed too early (use-after-free)

tests/run_tests.sh

@@ -35,6 +35,9 @@ SCHEME=ec ./test_snapshot.sh
 ./test_snapshot_chain.sh
 SCHEME=ec ./test_snapshot_chain.sh
 
+./test_snapshot_down.sh
+SCHEME=ec ./test_snapshot_down.sh
+
 ./test_splitbrain.sh
 
 ./test_rebalance_verify.sh

tests/test_snapshot_down.sh

@@ -0,0 +1,37 @@
+#!/bin/bash -ex
+
+. `dirname $0`/run_3osds.sh
+check_qemu
+
+# Test merge to child (without "inverse rename" optimisation)
+
+build/src/vitastor-cli --etcd_address $ETCD_URL create -s 128M testchain
+
+LD_PRELOAD="build/src/libfio_vitastor.so" \
+    fio -thread -name=test -ioengine=build/src/libfio_vitastor.so -bs=4M -direct=1 -iodepth=1 -fsync=1 -rw=write \
+        -etcd=$ETCD_URL -image=testchain -mirror_file=./testdata/mirror.bin
+
+# Create a snapshot
+build/src/vitastor-cli --etcd_address $ETCD_URL snap-create testchain@0
+
+# Write something to it
+LD_PRELOAD="build/src/libfio_vitastor.so" \
+fio -thread -name=test -ioengine=build/src/libfio_vitastor.so -bs=1M -direct=1 -iodepth=4 -rw=randwrite \
+    -randrepeat=0 -etcd=$ETCD_URL -image=testchain -number_ios=8 -mirror_file=./testdata/mirror.bin
+
+# Check the new content
+qemu-img convert -p \
+    -f raw "vitastor:etcd_host=127.0.0.1\:$ETCD_PORT/v3:image=testchain" \
+    -O raw ./testdata/layer1.bin
+cmp ./testdata/layer1.bin ./testdata/mirror.bin
+
+# Merge
+build/src/vitastor-cli --etcd_address $ETCD_URL rm testchain@0
+
+# Check the final image
+qemu-img convert -p \
+    -f raw "vitastor:etcd_host=127.0.0.1\:$ETCD_PORT/v3:image=testchain" \
+    -O raw ./testdata/layer1.bin
+cmp ./testdata/layer1.bin ./testdata/mirror.bin
+
+format_green OK