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) <[email protected]>

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.

> diff --git a/tools/testing/selftests/ftrace/boottime/tests/persistent-01-reserve-mem.sh b/tools/testing/selftests/ftrace/boottime/tests/persistent-01-reserve-mem.sh
> new file mode 100644
> index 0000000000000..49abaf518481f
> --- /dev/null
> +++ b/tools/testing/selftests/ftrace/boottime/tests/persistent-01-reserve-mem.sh
> @@ -0,0 +1,28 @@

[ ... ]

> +
> +# 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.

> +sleep 5
> +echo "FAIL: reboot trigger failed on first boot"
> +exit 1
> diff --git a/tools/testing/selftests/ftrace/boottime/tests/persistent-02-backup-instance.sh b/tools/testing/selftests/ftrace/boottime/tests/persistent-02-backup-instance.sh
> new file mode 100644
> index 0000000000000..0b2a2f03ce4f2
> --- /dev/null
> +++ b/tools/testing/selftests/ftrace/boottime/tests/persistent-02-backup-instance.sh
> @@ -0,0 +1,40 @@

[ ... ]

> +
> +# 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