[PATCH blktests 5/5] nvme/070: test for ABA ghost writes on a multipath fabrics namespace

[Mohamed Khalfella <mkhalfella@purestorage.com>]

An unacknowledged write that is retried on another path can still be
alive in the fabric. If it reaches the target after a later write to the
same LBA has landed, it overwrites it, and a read returns stale data.
Nothing in the tree exercises that window.

Add a test that builds it deliberately. A ublk loop device backs an
nvmet namespace exported through two ports, and the host connects to
both, so nvme-multipath has a second path to fail over to. io_timeout on
the subsystem drops to 2 seconds, then miniublk's inject command holds
one write in the backstore for 4 seconds. The host times that write out,
retries it on the other path, and the held write completes at the target
afterwards.

nvme-ghost-write-detector then writes distinct patterns to a single LBA
and reads the block back, so a resurfaced write shows up as the wrong
pattern.

The test requires nvme_core.multipath=Y and a fabrics transport. As of
today it passes on loop, which defines no timeout callback and so never
times the write out and never retries it, and fails on tcp, rdma and fc.

Signed-off-by: Mohamed Khalfella <mkhalfella@purestorage.com>
---
 tests/nvme/070     | 98 ++++++++++++++++++++++++++++++++++++++++++++++
 tests/nvme/070.out | 35 +++++++++++++++++
 2 files changed, 133 insertions(+)
 create mode 100755 tests/nvme/070
 create mode 100644 tests/nvme/070.out

diff --git a/tests/nvme/070 b/tests/nvme/070
new file mode 100755
index 0000000..e9a4690
--- /dev/null
+++ b/tests/nvme/070
@@ -0,0 +1,98 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-3.0+
+# Copyright (C) 2026 Mohamed Khalfella
+
+. tests/nvme/rc
+. common/ublk
+
+DESCRIPTION="Test injecting delay on nvme-target backstore and expect no corruption"
+
+requires() {
+	_nvme_requires
+	_have_loop
+	_have_ublk
+	_have_module_param_value nvme_core multipath Y
+	_require_nvme_trtype_is_fabrics
+	_have_src_program nvme-ghost-write-detector
+}
+
+set_conditions() {
+	_set_nvme_trtype "$@"
+}
+
+count_paths_to_subsystem() {
+	local subsysnqn="$1"
+	local dev count
+
+	count=0
+	for dev in /sys/class/nvme/nvme*; do
+		[[ -e "${dev}/subsysnqn" ]] || continue
+		[[ "$(cat "${dev}/subsysnqn")" == "${subsysnqn}" ]] || continue
+		count=$(( count + 1 ))
+	done
+	echo "${count}"
+}
+
+set_io_timeout_of_subsystem() {
+	local subsysnqn="$1"
+	local timeout="$2"
+	local dev
+
+	for dev in /sys/class/nvme/nvme*; do
+		[[ -e "${dev}/subsysnqn" ]] || continue
+		[[ "$(cat "${dev}/subsysnqn")" == "${subsysnqn}" ]] || continue
+		if ! echo "${timeout}" > "${dev}/io_timeout" 2> /dev/null; then
+			echo "FAIL: can not set io_timeout on ${dev##*/}"
+			return 1
+		fi
+	done
+}
+
+test() {
+	echo "Running ${TEST_NAME}"
+
+	local ns port nr_paths
+	local -a ports
+
+	if ! _init_ublk; then
+		return 1
+	fi
+
+	truncate -s "${NVME_IMG_SIZE}" "${TMPDIR}/ublk-img"
+	if ! ${UBLK_PROG} add -t loop -f "${TMPDIR}/ublk-img" -n 0 > "$FULL" 2>&1; then
+		echo "fail to add ublk device"
+		_exit_ublk
+		return 1
+	fi
+	udevadm settle
+
+	_setup_nvmet
+	_nvmet_target_setup --ports 2 --blkdev none
+	_create_nvmet_ns --blkdev /dev/ublkb0 \
+		--uuid "${def_subsys_uuid}" > /dev/null
+
+	_get_nvmet_ports "${def_subsysnqn}" ports
+	echo "Target ports: ${#ports[@]}"
+	for port in "${ports[@]}"; do
+		_nvme_connect_subsys --port "${port}"
+	done
+
+	nr_paths=$(count_paths_to_subsystem "${def_subsysnqn}")
+	if ((  nr_paths != 2 )); then
+		echo "FAIL: expected 2 paths, found ${nr_paths}"
+	fi
+
+	set_io_timeout_of_subsystem "${def_subsysnqn}" 2000
+
+	if ! ${UBLK_PROG} inject -n 0 -o write -d 4 -c 1 >> "$FULL" 2>&1; then
+		echo "FAIL: can not inject write delay"
+	fi
+
+	ns=$(_find_nvme_ns "${def_subsys_uuid}")
+	"$SRCDIR/nvme-ghost-write-detector" "/dev/${ns}"
+
+	_nvme_disconnect_subsys
+	_nvmet_target_cleanup
+	_exit_ublk
+	echo "Test complete"
+}
diff --git a/tests/nvme/070.out b/tests/nvme/070.out
new file mode 100644
index 0000000..b43fec7
--- /dev/null
+++ b/tests/nvme/070.out
@@ -0,0 +1,35 @@
+Running nvme/070
+Target ports: 2
+starting nvme-ghost-write-detector test program
+iteration number 0, writing data
+validating written data
+successfully validated
+iteration number 1, writing data
+validating written data
+successfully validated
+iteration number 2, writing data
+validating written data
+successfully validated
+iteration number 3, writing data
+validating written data
+successfully validated
+iteration number 4, writing data
+validating written data
+successfully validated
+iteration number 5, writing data
+validating written data
+successfully validated
+iteration number 6, writing data
+validating written data
+successfully validated
+iteration number 7, writing data
+validating written data
+successfully validated
+iteration number 8, writing data
+validating written data
+successfully validated
+iteration number 9, writing data
+validating written data
+successfully validated
+finished nvme-ghost-write-detector test program
+Test complete
-- 
2.55.0