[PATCH 2/2] selftests/mm: add kmemleak verbose dedup test

Breno Leitao
2026-04-21T13:45:39Z

Exercise the per-scan dedup of kmemleak's verbose leak output added in
the previous commit. The test depends on the kmemleak-test sample
module (CONFIG_SAMPLE_KMEMLEAK=m); load it and unload it to orphan ten
list entries from a single kzalloc() call site that all share one
stackdepot trace_handle, trigger two scans, and assert that the number
of "unreferenced object" lines printed in dmesg is strictly less than
the number of leaks reported. Skip cleanly when kmemleak is absent,
disabled at runtime, or CONFIG_SAMPLE_KMEMLEAK is not built in.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
tools/testing/selftests/mm/test_kmemleak_dedup.sh | 86 +++++++++++++++++++++++
1 file changed, 86 insertions(+)

diff --git a/tools/testing/selftests/mm/test_kmemleak_dedup.sh b/tools/testing/selftests/mm/test_kmemleak_dedup.sh
new file mode 100755
index 0000000000000..1a1b6efd6470a
--- /dev/null
+++ b/tools/testing/selftests/mm/test_kmemleak_dedup.sh
@@ -0,0 +1,86 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Verify that kmemleak's verbose scan output deduplicates leaks that share
+# the same allocation backtrace. The kmemleak-test module leaks 10 list
+# entries from a single kzalloc() call site, so they share one stackdepot
+# trace_handle. With dedup, only one "unreferenced object" line should be
+# printed for that backtrace per scan, while the per-scan leak counter
+# still accounts for every object.
+#
+# The expected output is something like:
+# PASS: kmemleak verbose output deduplicated (11 printed for 61 leaks)
+#
+# Author: Breno Leitao <leitao@debian.org>
+
+ksft_skip=4
+KMEMLEAK=/sys/kernel/debug/kmemleak
+VERBOSE_PARAM=/sys/module/kmemleak/parameters/verbose
+MODULE=kmemleak-test
+
+skip() {
+ echo "SKIP: $*"
+ exit $ksft_skip
+}
+
+fail() {
+ echo "FAIL: $*"
+ exit 1
+}
+
+[ "$(id -u)" -eq 0 ] || skip "must run as root"
+[ -r "$KMEMLEAK" ] || skip "no kmemleak debugfs (CONFIG_DEBUG_KMEMLEAK)"
+[ -w "$VERBOSE_PARAM" ] || skip "kmemleak verbose param missing"
+modinfo "$MODULE" >/dev/null 2>&1 ||
+ skip "$MODULE not built (CONFIG_SAMPLE_KMEMLEAK)"
+
+# kmemleak can be present but disabled at runtime (boot arg kmemleak=off,
+# or it self-disabled after an internal error). In that state writes other
+# than "clear" return EPERM, so probe once and skip if so.
+if ! echo scan > "$KMEMLEAK" 2>/dev/null; then
+ skip "kmemleak is disabled (check dmesg or kmemleak= boot arg)"
+fi
+
+prev_verbose=$(cat "$VERBOSE_PARAM")
+cleanup() {
+ echo "$prev_verbose" > "$VERBOSE_PARAM" 2>/dev/null
+ rmmod "$MODULE" 2>/dev/null
+}
+trap cleanup EXIT
+
+echo 1 > "$VERBOSE_PARAM"
+
+# Drain the existing leak set so the next scan only reports our objects.
+echo clear > "$KMEMLEAK"
+
+modprobe "$MODULE" || fail "failed to load $MODULE"
+# Removing the module orphans the list elements without freeing them.
+rmmod "$MODULE" || fail "failed to unload $MODULE"
+
+# Two scans: kmemleak requires the object to survive a full scan cycle
+# before it is reported as unreferenced.
+dmesg -C >/dev/null
+echo scan > "$KMEMLEAK"; sleep 6
+echo scan > "$KMEMLEAK"; sleep 6
+
+log=$(dmesg)
+
+new_leaks=$(echo "$log" |
+ sed -n 's/.*kmemleak: \([0-9]\+\) new suspected.*/\1/p' | tail -1)
+[ -n "$new_leaks" ] || fail "no 'new suspected memory leaks' line found"
+
+# Count "unreferenced object" lines emitted in verbose output.
+printed=$(echo "$log" | grep -c 'kmemleak: unreferenced object')
+
+echo "new_leaks=$new_leaks printed=$printed"
+
+# The kzalloc(sizeof(*elem)) loop alone contributes 10 leaks sharing one
+# backtrace, so without dedup printed >= 10. With dedup the printed count
+# must be strictly less than the reported leak total.
+[ "$new_leaks" -ge 10 ] || fail "expected >=10 new leaks, got $new_leaks"
+[ "$printed" -lt "$new_leaks" ] || \
+ fail "no dedup: printed=$printed new_leaks=$new_leaks"
+
+echo "PASS: kmemleak verbose output deduplicated" \
+ "($printed printed for $new_leaks leaks)"
+exit 0

--
2.52.0