[PATCH] workqueue: forbid TEST_WORKQUEUE from being built-in

[Breno Leitao <leitao@debian.org>]

The benchmark drives the workqueue's affinity_scope through sysfs by
filp_open()'ing /sys/bus/workqueue/devices/bench_wq/affinity_scope. When
CONFIG_TEST_WORKQUEUE=y, the module_init runs during kernel init before
userspace has mounted sysfs, so every open returns -ENOENT and the
benchmark loop spins emitting:

  test_workqueue: open /sys/bus/workqueue/devices/bench_wq/affinity_scope failed: -2

Mirror the TEST_BPF pattern and add "depends on m" so Kconfig will not
let this be built into the kernel image, and document the reason in the
help text.

Fixes: 24b2e73f9700 ("workqueue: add test_workqueue benchmark module")
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 lib/Kconfig.debug | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 9d54c48d7d982..9dfe6e16de91b 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2666,12 +2666,17 @@ config TEST_VMALLOC
 
 config TEST_WORKQUEUE
 	tristate "Test module for stress/performance analysis of workqueue"
+	depends on m
 	default n
 	help
 	  This builds the "test_workqueue" module for benchmarking
 	  workqueue throughput under contention. Useful for evaluating
 	  affinity scope changes (e.g., cache_shard vs cache).
 
+	  The test drives sysfs to switch affinity scopes, so it must be
+	  loaded after userspace has mounted sysfs; building it in (=y)
+	  would run module_init before /sys is available.
+
 	  If unsure, say N.
 
 config TEST_BPF

---
base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83
change-id: 20260511-workqueue_fix_test-eb1134cb7237

Best regards,
--  
Breno Leitao <leitao@debian.org>