Re: [PATCH v3 4/4] selftests/ftrace: Add persistent ring buffer testcases

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Test enters an infinite reboot loop if the persistent trace feature fails.
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--- Patch [4]: [PATCH v3 4/4] selftests/ftrace: Add persistent ring buffer testcases ---

commit d365a5483f67b1295e536e6d26fd4ee7166e27b3
Author: Masami Hiramatsu (Google) [off-list ref]

selftests/ftrace: Add persistent ring buffer testcases

Add test cases for persistent ring buffer and backup instance across guest
crash/reboot. These verify trace data retention in the boot_map instance and
preservation in the backup instance on subsequent boot.

[ ... ]

+
+# Check if Boot 1 marker was already written
+if grep -q "BOOT1_MARKER" "$TRACEDIR/instances/boot_map/trace" 2>/dev/null; then
+	# Second boot: verify persistent ring buffer content from first boot
+	echo "PASS: persistent-01-reserve-mem"
+	exit 0
+fi
+
+# First boot: write marker to persistent buffer and trigger kernel crash/reboot
+echo "BOOT1_MARKER" > "$TRACEDIR/instances/boot_map/trace_marker"
+sync
+
+# Trigger reboot to restart into second boot
+echo b > /proc/sysrq-trigger 2>/dev/null || echo c > /proc/sysrq-trigger 2>/dev/null || true

[Severity: Medium]
If the persistent trace feature fails to retain the BOOT1_MARKER across
reboot, could this script enter an infinite reboot loop?

Since the test falls through to the first-boot logic when the marker is
missing, it appears it will write the marker and reboot again indefinitely.
This might cause the test to run until it is killed by a global timeout
rather than failing cleanly.

[ ... ]

+
+# Check if BOOT1_MARKER is in boot_map/trace (indicates second boot)
+if grep -q "BOOT1_MARKER" "$TRACEDIR/instances/boot_map/trace" 2>/dev/null; then
+	# Second boot: verify BOOT1_MARKER was copied into backup/trace from Boot 1
+	if grep -q "BOOT1_MARKER" "$TRACEDIR/instances/backup/trace" 2>/dev/null; then
+		echo "PASS: persistent-02-backup-instance"
+		exit 0
+	else
+		echo "FAIL: BOOT1_MARKER found in boot_map/trace" \
+			"but missing from backup/trace on second boot"
+		exit 1
+	fi
+fi
+
+# First boot: write BOOT1_MARKER to boot_map and reboot via sysrq-trigger
+echo "BOOT1_MARKER" > "$TRACEDIR/instances/boot_map/trace_marker"
+sync
+
+# Trigger reboot to restart into second boot
+echo b > /proc/sysrq-trigger 2>/dev/null || echo c > /proc/sysrq-trigger 2>/dev/null || true

[Severity: Medium]
Similarly, does this script also risk an infinite reboot loop if the marker
is missing from boot_map/trace on the second boot?

It looks like it would also fall back to triggering another reboot instead
of reporting a failure.

+sleep 5
+echo "FAIL: reboot trigger failed on first boot"
+exit 1

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Sashiko AI review · https://sashiko.dev/#/patchset/178649540853.438282.4271870161169100680.stgit@devnote2?part=4