[PATCH V2 0/2] slub_kunit: add a test case for {kmalloc,kfree}_nolock

[PATCH V2 0/2] slub_kunit: add a test case for {kmalloc,kfree}_nolock

[Harry Yoo (Oracle)]

Test bots don't seem to test kmalloc_nolock() and kfree_nolock(), so
subtle bugs are discovered late. To make it easier to test, add a kunit
test case that stresses these paths by combining a tight alloc/free loop
with perf-triggered interrupts that invoke {kmalloc,kfree}_nolock() from
the overflow handler.

While at it, also add the missing MAINTAINERS entry for slub_kunit.c.

v1->v2:
  - Fix build errors on arches without CONFIG_PERF_EVENTS (Thanks
    Vlastimil)
  - Rename some identifiers
  - Use GFP_KERNEL_ACCOUNT or GFP_KERNEL for kmalloc(), instead of 0 or
    __GFP_ACCOUNT (that was unnecessarily restrictive).

p.s. I was writing this test while developing kvfree_rcu_nolock(),
let's add a test case in advance.

Probably a similar test case for the page allocator is worth adding
but I'm not sure where the right place would be.

v1: https://lore.kernel.org/linux-mm/20260330120517.104743-1-harry@kernel.org

Harry Yoo (Oracle) (2):
  MAINTAINERS: add lib/tests/slub_kunit.c to SLAB ALLOCATOR section
  lib/tests/slub_kunit: add a test case for {kmalloc,kfree}_nolock

 MAINTAINERS            |  1 +
 lib/tests/slub_kunit.c | 92 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 93 insertions(+)


base-commit: dbc785fb4d9cfa0115e69e614fe20b4ab90f8366
-- 
2.43.0

[PATCH V2 1/2] MAINTAINERS: add lib/tests/slub_kunit.c to SLAB ALLOCATOR section

[Harry Yoo (Oracle)]

The slub_kunit module has been maintained by SLAB ALLOCATOR folks,
but is missing in the MAINTAINERS file. Add the missing entry.

Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Harry Yoo (Oracle) <harry@kernel.org>
---
 MAINTAINERS | 1 +
 1 file changed, 1 insertion(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 96ea84948d76..5f5add4f72a0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24354,6 +24354,7 @@ F:	Documentation/admin-guide/mm/slab.rst
 F:	Documentation/mm/slab.rst
 F:	include/linux/mempool.h
 F:	include/linux/slab.h
+F:	lib/tests/slub_kunit.c
 F:	mm/failslab.c
 F:	mm/mempool.c
 F:	mm/slab.h
-- 
2.43.0

[PATCH V2 2/2] lib/tests/slub_kunit: add a test case for {kmalloc,kfree}_nolock

[Harry Yoo (Oracle)]

Testing invocation of {kmalloc,kfree}_nolock() during kmalloc() or
kfree() is tricky, and it is even harder to ensure that slowpaths are
properly tested. Lack of such testing has led to late discovery of
the bug fixed by commit a1e244a9f177 ("mm/slab: use prandom if
!allow_spin").

Add a slub_kunit test that allocates and frees objects in a tight loop
while a perf event triggers interrupts (NMI or hardirq depending on
the arch) on the same task, invoking {kmalloc,kfree}_nolock() from the
overflow handler.

Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Harry Yoo (Oracle) <harry@kernel.org>
---
 lib/tests/slub_kunit.c | 92 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)

diff --git a/lib/tests/slub_kunit.c b/lib/tests/slub_kunit.c
index 848b682a2d70..fa6d31dbca16 100644
--- a/lib/tests/slub_kunit.c
+++ b/lib/tests/slub_kunit.c
@@ -7,6 +7,7 @@
 #include <linux/kernel.h>
 #include <linux/rcupdate.h>
 #include <linux/delay.h>
+#include <linux/perf_event.h>
 #include "../mm/slab.h"
 
 static struct kunit_resource resource;
@@ -291,6 +292,94 @@ static void test_krealloc_redzone_zeroing(struct kunit *test)
 	kmem_cache_destroy(s);
 }
 
+#ifdef CONFIG_PERF_EVENTS
+#define NR_ITERATIONS 1000
+#define NR_OBJECTS 1000
+static void *objects[NR_OBJECTS];
+
+struct test_nolock_context {
+	struct kunit *test;
+	int callback_count;
+	int alloc_ok;
+	int alloc_fail;
+	struct perf_event *event;
+};
+
+static struct perf_event_attr hw_attr = {
+	.type = PERF_TYPE_HARDWARE,
+	.config = PERF_COUNT_HW_CPU_CYCLES,
+	.size = sizeof(struct perf_event_attr),
+	.pinned = 1,
+	.disabled = 1,
+	.freq = 1,
+	.sample_freq = 100000,
+};
+
+static void overflow_handler_test_kmalloc_kfree_nolock(struct perf_event *event,
+						       struct perf_sample_data *data,
+						       struct pt_regs *regs)
+{
+	void *objp;
+	gfp_t gfp;
+	struct test_nolock_context *ctx = event->overflow_handler_context;
+
+	/* __GFP_ACCOUNT to test kmalloc_nolock() in alloc_slab_obj_exts() */
+	gfp = (ctx->callback_count % 2) ? 0 : __GFP_ACCOUNT;
+	objp = kmalloc_nolock(64, gfp, NUMA_NO_NODE);
+
+	if (objp)
+		ctx->alloc_ok++;
+	else
+		ctx->alloc_fail++;
+
+	kfree_nolock(objp);
+	ctx->callback_count++;
+}
+
+static void test_kmalloc_kfree_nolock(struct kunit *test)
+{
+	int i, j;
+	struct test_nolock_context ctx = { .test = test };
+	struct perf_event *event;
+	bool alloc_fail = false;
+
+	event = perf_event_create_kernel_counter(&hw_attr, -1, current,
+						 overflow_handler_test_kmalloc_kfree_nolock,
+						 &ctx);
+	if (IS_ERR(event))
+		kunit_skip(test, "Failed to create perf event");
+	ctx.event = event;
+	perf_event_enable(ctx.event);
+	for (i = 0; i < NR_ITERATIONS; i++) {
+		for (j = 0; j < NR_OBJECTS; j++) {
+			gfp_t gfp = (i % 2) ? GFP_KERNEL : GFP_KERNEL_ACCOUNT;
+
+			objects[j] = kmalloc(64, gfp);
+			if (!objects[j]) {
+				j--;
+				while (j >= 0)
+					kfree(objects[j--]);
+				alloc_fail = true;
+				goto cleanup;
+			}
+		}
+		for (j = 0; j < NR_OBJECTS; j++)
+			kfree(objects[j]);
+	}
+
+cleanup:
+	perf_event_disable(ctx.event);
+	perf_event_release_kernel(ctx.event);
+
+	kunit_info(test, "callback_count: %d, alloc_ok: %d, alloc_fail: %d\n",
+		   ctx.callback_count, ctx.alloc_ok, ctx.alloc_fail);
+
+	if (alloc_fail)
+		kunit_skip(test, "Allocation failed");
+	KUNIT_EXPECT_EQ(test, 0, slab_errors);
+}
+#endif
+
 static int test_init(struct kunit *test)
 {
 	slab_errors = 0;
@@ -315,6 +404,9 @@ static struct kunit_case test_cases[] = {
 	KUNIT_CASE(test_kfree_rcu_wq_destroy),
 	KUNIT_CASE(test_leak_destroy),
 	KUNIT_CASE(test_krealloc_redzone_zeroing),
+#ifdef CONFIG_PERF_EVENTS
+	KUNIT_CASE_SLOW(test_kmalloc_kfree_nolock),
+#endif
 	{}
 };
 
-- 
2.43.0