sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 585 insertions, 0 deletions

diff --git a/init/initramfs_test.c b/init/initramfs_test.c
new file mode 100644
index 000000000..bc55306d2
--- /dev/null
+++ b/init/initramfs_test.c
@@ -0,0 +1,585 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <kunit/test.h>
+#include <linux/fcntl.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/init_syscalls.h>
+#include <linux/initrd.h>
+#include <linux/stringify.h>
+#include <linux/timekeeping.h>
+#include "initramfs_internal.h"
+
+struct initramfs_test_cpio {
+	char *magic;
+	unsigned int ino;
+	unsigned int mode;
+	unsigned int uid;
+	unsigned int gid;
+	unsigned int nlink;
+	unsigned int mtime;
+	unsigned int filesize;
+	unsigned int devmajor;
+	unsigned int devminor;
+	unsigned int rdevmajor;
+	unsigned int rdevminor;
+	unsigned int namesize;
+	unsigned int csum;
+	char *fname;
+	char *data;
+};
+
+/* regular newc header format */
+#define CPIO_HDR_FMT "%s%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%s"
+/*
+ * Bogus newc header with "0x" prefixes on the uid, gid, and namesize values.
+ * parse_header()/simple_str[n]toul() accepted this, contrary to the initramfs
+ * specification. hex2bin() now fails.
+ */
+#define CPIO_HDR_OX_INJECT \
+	"%s%08x%08x0x%06x0X%06x%08x%08x%08x%08x%08x%08x%08x0x%06x%08x%s"
+
+static size_t fill_cpio(struct initramfs_test_cpio *cs, size_t csz,
+			bool inject_ox, char *out)
+{
+	int i;
+	size_t off = 0;
+
+	for (i = 0; i < csz; i++) {
+		char *pos = &out[off];
+		struct initramfs_test_cpio *c = &cs[i];
+		size_t thislen;
+
+		/* +1 to account for nulterm */
+		thislen = sprintf(pos,
+			inject_ox ? CPIO_HDR_OX_INJECT : CPIO_HDR_FMT,
+			c->magic, c->ino, c->mode, c->uid, c->gid, c->nlink,
+			c->mtime, c->filesize, c->devmajor, c->devminor,
+			c->rdevmajor, c->rdevminor, c->namesize, c->csum,
+			c->fname) + 1;
+
+		pr_debug("packing (%zu): %.*s\n", thislen, (int)thislen, pos);
+		if (thislen != CPIO_HDRLEN + c->namesize)
+			pr_debug("padded to: %u\n", CPIO_HDRLEN + c->namesize);
+		off += CPIO_HDRLEN + c->namesize;
+		while (off & 3)
+			out[off++] = '\0';
+
+		memcpy(&out[off], c->data, c->filesize);
+		off += c->filesize;
+		while (off & 3)
+			out[off++] = '\0';
+	}
+
+	return off;
+}
+
+static void __init initramfs_test_extract(struct kunit *test)
+{
+	char *err, *cpio_srcbuf;
+	size_t len;
+	struct timespec64 ts_before, ts_after;
+	struct kstat st = {};
+	struct initramfs_test_cpio c[] = { {
+		.magic = "070701",
+		.ino = 1,
+		.mode = S_IFREG | 0777,
+		.uid = 12,
+		.gid = 34,
+		.nlink = 1,
+		.mtime = 56,
+		.filesize = 0,
+		.devmajor = 0,
+		.devminor = 1,
+		.rdevmajor = 0,
+		.rdevminor = 0,
+		.namesize = sizeof("initramfs_test_extract"),
+		.csum = 0,
+		.fname = "initramfs_test_extract",
+	}, {
+		.magic = "070701",
+		.ino = 2,
+		.mode = S_IFDIR | 0777,
+		.nlink = 1,
+		.mtime = 57,
+		.devminor = 1,
+		.namesize = sizeof("initramfs_test_extract_dir"),
+		.fname = "initramfs_test_extract_dir",
+	}, {
+		.magic = "070701",
+		.namesize = sizeof("TRAILER!!!"),
+		.fname = "TRAILER!!!",
+	} };
+
+	/* +3 to cater for any 4-byte end-alignment */
+	cpio_srcbuf = kzalloc(ARRAY_SIZE(c) * (CPIO_HDRLEN + PATH_MAX + 3),
+			      GFP_KERNEL);
+	len = fill_cpio(c, ARRAY_SIZE(c), false, cpio_srcbuf);
+
+	ktime_get_real_ts64(&ts_before);
+	err = unpack_to_rootfs(cpio_srcbuf, len);
+	ktime_get_real_ts64(&ts_after);
+	if (err) {
+		KUNIT_FAIL(test, "unpack failed %s", err);
+		goto out;
+	}
+
+	KUNIT_EXPECT_EQ(test, init_stat(c[0].fname, &st, 0), 0);
+	KUNIT_EXPECT_TRUE(test, S_ISREG(st.mode));
+	KUNIT_EXPECT_TRUE(test, uid_eq(st.uid, KUIDT_INIT(c[0].uid)));
+	KUNIT_EXPECT_TRUE(test, gid_eq(st.gid, KGIDT_INIT(c[0].gid)));
+	KUNIT_EXPECT_EQ(test, st.nlink, 1);
+	if (IS_ENABLED(CONFIG_INITRAMFS_PRESERVE_MTIME)) {
+		KUNIT_EXPECT_EQ(test, st.mtime.tv_sec, c[0].mtime);
+	} else {
+		KUNIT_EXPECT_GE(test, st.mtime.tv_sec, ts_before.tv_sec);
+		KUNIT_EXPECT_LE(test, st.mtime.tv_sec, ts_after.tv_sec);
+	}
+	KUNIT_EXPECT_EQ(test, st.blocks, c[0].filesize);
+
+	KUNIT_EXPECT_EQ(test, init_stat(c[1].fname, &st, 0), 0);
+	KUNIT_EXPECT_TRUE(test, S_ISDIR(st.mode));
+	if (IS_ENABLED(CONFIG_INITRAMFS_PRESERVE_MTIME)) {
+		KUNIT_EXPECT_EQ(test, st.mtime.tv_sec, c[1].mtime);
+	} else {
+		KUNIT_EXPECT_GE(test, st.mtime.tv_sec, ts_before.tv_sec);
+		KUNIT_EXPECT_LE(test, st.mtime.tv_sec, ts_after.tv_sec);
+	}
+
+	KUNIT_EXPECT_EQ(test, init_unlink(c[0].fname), 0);
+	KUNIT_EXPECT_EQ(test, init_rmdir(c[1].fname), 0);
+out:
+	kfree(cpio_srcbuf);
+}
+
+/*
+ * Don't terminate filename. Previously, the cpio filename field was passed
+ * directly to filp_open(collected, O_CREAT|..) without nulterm checks. See
+ * https://lore.kernel.org/linux-fsdevel/20241030035509.20194-2-ddiss@suse.de
+ */
+static void __init initramfs_test_fname_overrun(struct kunit *test)
+{
+	char *err, *cpio_srcbuf;
+	size_t len, suffix_off;
+	struct initramfs_test_cpio c[] = { {
+		.magic = "070701",
+		.ino = 1,
+		.mode = S_IFREG | 0777,
+		.uid = 0,
+		.gid = 0,
+		.nlink = 1,
+		.mtime = 1,
+		.filesize = 0,
+		.devmajor = 0,
+		.devminor = 1,
+		.rdevmajor = 0,
+		.rdevminor = 0,
+		.namesize = sizeof("initramfs_test_fname_overrun"),
+		.csum = 0,
+		.fname = "initramfs_test_fname_overrun",
+	} };
+
+	/*
+	 * poison cpio source buffer, so we can detect overrun. source
+	 * buffer is used by read_into() when hdr or fname
+	 * are already available (e.g. no compression).
+	 */
+	cpio_srcbuf = kmalloc(CPIO_HDRLEN + PATH_MAX + 3, GFP_KERNEL);
+	memset(cpio_srcbuf, 'B', CPIO_HDRLEN + PATH_MAX + 3);
+	/* limit overrun to avoid crashes / filp_open() ENAMETOOLONG */
+	cpio_srcbuf[CPIO_HDRLEN + strlen(c[0].fname) + 20] = '\0';
+
+	len = fill_cpio(c, ARRAY_SIZE(c), false, cpio_srcbuf);
+	/* overwrite trailing fname terminator and padding */
+	suffix_off = len - 1;
+	while (cpio_srcbuf[suffix_off] == '\0') {
+		cpio_srcbuf[suffix_off] = 'P';
+		suffix_off--;
+	}
+
+	err = unpack_to_rootfs(cpio_srcbuf, len);
+	KUNIT_EXPECT_NOT_NULL(test, err);
+
+	kfree(cpio_srcbuf);
+}
+
+static void __init initramfs_test_data(struct kunit *test)
+{
+	char *err, *cpio_srcbuf;
+	size_t len;
+	struct file *file;
+	struct initramfs_test_cpio c[] = { {
+		.magic = "070701",
+		.ino = 1,
+		.mode = S_IFREG | 0777,
+		.uid = 0,
+		.gid = 0,
+		.nlink = 1,
+		.mtime = 1,
+		.filesize = sizeof("ASDF") - 1,
+		.devmajor = 0,
+		.devminor = 1,
+		.rdevmajor = 0,
+		.rdevminor = 0,
+		.namesize = sizeof("initramfs_test_data"),
+		.csum = 0,
+		.fname = "initramfs_test_data",
+		.data = "ASDF",
+	} };
+
+	/* +6 for max name and data 4-byte padding */
+	cpio_srcbuf = kmalloc(CPIO_HDRLEN + c[0].namesize + c[0].filesize + 6,
+			      GFP_KERNEL);
+
+	len = fill_cpio(c, ARRAY_SIZE(c), false, cpio_srcbuf);
+
+	err = unpack_to_rootfs(cpio_srcbuf, len);
+	KUNIT_EXPECT_NULL(test, err);
+
+	file = filp_open(c[0].fname, O_RDONLY, 0);
+	if (IS_ERR(file)) {
+		KUNIT_FAIL(test, "open failed");
+		goto out;
+	}
+
+	/* read back file contents into @cpio_srcbuf and confirm match */
+	len = kernel_read(file, cpio_srcbuf, c[0].filesize, NULL);
+	KUNIT_EXPECT_EQ(test, len, c[0].filesize);
+	KUNIT_EXPECT_MEMEQ(test, cpio_srcbuf, c[0].data, len);
+
+	fput(file);
+	KUNIT_EXPECT_EQ(test, init_unlink(c[0].fname), 0);
+out:
+	kfree(cpio_srcbuf);
+}
+
+static void __init initramfs_test_csum(struct kunit *test)
+{
+	char *err, *cpio_srcbuf;
+	size_t len;
+	struct initramfs_test_cpio c[] = { {
+		/* 070702 magic indicates a valid csum is present */
+		.magic = "070702",
+		.ino = 1,
+		.mode = S_IFREG | 0777,
+		.nlink = 1,
+		.filesize = sizeof("ASDF") - 1,
+		.devminor = 1,
+		.namesize = sizeof("initramfs_test_csum"),
+		.csum = 'A' + 'S' + 'D' + 'F',
+		.fname = "initramfs_test_csum",
+		.data = "ASDF",
+	}, {
+		/* mix csum entry above with no-csum entry below */
+		.magic = "070701",
+		.ino = 2,
+		.mode = S_IFREG | 0777,
+		.nlink = 1,
+		.filesize = sizeof("ASDF") - 1,
+		.devminor = 1,
+		.namesize = sizeof("initramfs_test_csum_not_here"),
+		/* csum ignored */
+		.csum = 5555,
+		.fname = "initramfs_test_csum_not_here",
+		.data = "ASDF",
+	} };
+
+	cpio_srcbuf = kmalloc(8192, GFP_KERNEL);
+
+	len = fill_cpio(c, ARRAY_SIZE(c), false, cpio_srcbuf);
+
+	err = unpack_to_rootfs(cpio_srcbuf, len);
+	KUNIT_EXPECT_NULL(test, err);
+
+	KUNIT_EXPECT_EQ(test, init_unlink(c[0].fname), 0);
+	KUNIT_EXPECT_EQ(test, init_unlink(c[1].fname), 0);
+
+	/* mess up the csum and confirm that unpack fails */
+	c[0].csum--;
+	len = fill_cpio(c, ARRAY_SIZE(c), false, cpio_srcbuf);
+
+	err = unpack_to_rootfs(cpio_srcbuf, len);
+	KUNIT_EXPECT_NOT_NULL(test, err);
+
+	/*
+	 * file (with content) is still retained in case of bad-csum abort.
+	 * Perhaps we should change this.
+	 */
+	KUNIT_EXPECT_EQ(test, init_unlink(c[0].fname), 0);
+	KUNIT_EXPECT_EQ(test, init_unlink(c[1].fname), -ENOENT);
+	kfree(cpio_srcbuf);
+}
+
+/*
+ * hardlink hashtable may leak when the archive omits a trailer:
+ * https://lore.kernel.org/r/20241107002044.16477-10-ddiss@suse.de/
+ */
+static void __init initramfs_test_hardlink(struct kunit *test)
+{
+	char *err, *cpio_srcbuf;
+	size_t len;
+	struct kstat st0 = {}, st1 = {};
+	struct initramfs_test_cpio c[] = { {
+		.magic = "070701",
+		.ino = 1,
+		.mode = S_IFREG | 0777,
+		.nlink = 2,
+		.devminor = 1,
+		.namesize = sizeof("initramfs_test_hardlink"),
+		.fname = "initramfs_test_hardlink",
+	}, {
+		/* hardlink data is present in last archive entry */
+		.magic = "070701",
+		.ino = 1,
+		.mode = S_IFREG | 0777,
+		.nlink = 2,
+		.filesize = sizeof("ASDF") - 1,
+		.devminor = 1,
+		.namesize = sizeof("initramfs_test_hardlink_link"),
+		.fname = "initramfs_test_hardlink_link",
+		.data = "ASDF",
+	} };
+
+	cpio_srcbuf = kmalloc(8192, GFP_KERNEL);
+
+	len = fill_cpio(c, ARRAY_SIZE(c), false, cpio_srcbuf);
+
+	err = unpack_to_rootfs(cpio_srcbuf, len);
+	KUNIT_EXPECT_NULL(test, err);
+
+	KUNIT_EXPECT_EQ(test, init_stat(c[0].fname, &st0, 0), 0);
+	KUNIT_EXPECT_EQ(test, init_stat(c[1].fname, &st1, 0), 0);
+	KUNIT_EXPECT_EQ(test, st0.ino, st1.ino);
+	KUNIT_EXPECT_EQ(test, st0.nlink, 2);
+	KUNIT_EXPECT_EQ(test, st1.nlink, 2);
+
+	KUNIT_EXPECT_EQ(test, init_unlink(c[0].fname), 0);
+	KUNIT_EXPECT_EQ(test, init_unlink(c[1].fname), 0);
+
+	kfree(cpio_srcbuf);
+}
+
+#define INITRAMFS_TEST_MANY_LIMIT 1000
+#define INITRAMFS_TEST_MANY_PATH_MAX (sizeof("initramfs_test_many-") \
+			+ sizeof(__stringify(INITRAMFS_TEST_MANY_LIMIT)))
+static void __init initramfs_test_many(struct kunit *test)
+{
+	char *err, *cpio_srcbuf, *p;
+	size_t len = INITRAMFS_TEST_MANY_LIMIT *
+		     (CPIO_HDRLEN + INITRAMFS_TEST_MANY_PATH_MAX + 3);
+	char thispath[INITRAMFS_TEST_MANY_PATH_MAX];
+	int i;
+
+	p = cpio_srcbuf = kmalloc(len, GFP_KERNEL);
+
+	for (i = 0; i < INITRAMFS_TEST_MANY_LIMIT; i++) {
+		struct initramfs_test_cpio c = {
+			.magic = "070701",
+			.ino = i,
+			.mode = S_IFREG | 0777,
+			.nlink = 1,
+			.devminor = 1,
+			.fname = thispath,
+		};
+
+		c.namesize = 1 + sprintf(thispath, "initramfs_test_many-%d", i);
+		p += fill_cpio(&c, 1, false, p);
+	}
+
+	len = p - cpio_srcbuf;
+	err = unpack_to_rootfs(cpio_srcbuf, len);
+	KUNIT_EXPECT_NULL(test, err);
+
+	for (i = 0; i < INITRAMFS_TEST_MANY_LIMIT; i++) {
+		sprintf(thispath, "initramfs_test_many-%d", i);
+		KUNIT_EXPECT_EQ(test, init_unlink(thispath), 0);
+	}
+
+	kfree(cpio_srcbuf);
+}
+
+/*
+ * An initramfs filename is namesize in length, including the zero-terminator.
+ * A filename can be zero-terminated prior to namesize, with the remainder used
+ * as padding. This can be useful for e.g. alignment of file data segments with
+ * a 4KB filesystem block, allowing for extent sharing (reflinks) between cpio
+ * source and destination. This hack works with both GNU cpio and initramfs, as
+ * long as PATH_MAX isn't exceeded.
+ */
+static void __init initramfs_test_fname_pad(struct kunit *test)
+{
+	char *err;
+	size_t len;
+	struct file *file;
+	char fdata[] = "this file data is aligned at 4K in the archive";
+	struct test_fname_pad {
+		char padded_fname[4096 - CPIO_HDRLEN];
+		char cpio_srcbuf[CPIO_HDRLEN + PATH_MAX + 3 + sizeof(fdata)];
+	} *tbufs = kzalloc_obj(struct test_fname_pad);
+	struct initramfs_test_cpio c[] = { {
+		.magic = "070701",
+		.ino = 1,
+		.mode = S_IFREG | 0777,
+		.uid = 0,
+		.gid = 0,
+		.nlink = 1,
+		.mtime = 1,
+		.filesize = sizeof(fdata),
+		.devmajor = 0,
+		.devminor = 1,
+		.rdevmajor = 0,
+		.rdevminor = 0,
+		/* align file data at 4K archive offset via padded fname */
+		.namesize = 4096 - CPIO_HDRLEN,
+		.csum = 0,
+		.fname = tbufs->padded_fname,
+		.data = fdata,
+	} };
+
+	memcpy(tbufs->padded_fname, "padded_fname", sizeof("padded_fname"));
+	len = fill_cpio(c, ARRAY_SIZE(c), false, tbufs->cpio_srcbuf);
+
+	err = unpack_to_rootfs(tbufs->cpio_srcbuf, len);
+	KUNIT_EXPECT_NULL(test, err);
+
+	file = filp_open(c[0].fname, O_RDONLY, 0);
+	if (IS_ERR(file)) {
+		KUNIT_FAIL(test, "open failed");
+		goto out;
+	}
+
+	/* read back file contents into @cpio_srcbuf and confirm match */
+	len = kernel_read(file, tbufs->cpio_srcbuf, c[0].filesize, NULL);
+	KUNIT_EXPECT_EQ(test, len, c[0].filesize);
+	KUNIT_EXPECT_MEMEQ(test, tbufs->cpio_srcbuf, c[0].data, len);
+
+	fput(file);
+	KUNIT_EXPECT_EQ(test, init_unlink(c[0].fname), 0);
+out:
+	kfree(tbufs);
+}
+
+static void __init initramfs_test_fname_path_max(struct kunit *test)
+{
+	char *err;
+	size_t len;
+	struct kstat st0 = {}, st1 = {};
+	char fdata[] = "this file data will not be unpacked";
+	struct test_fname_path_max {
+		char fname_oversize[PATH_MAX + 1];
+		char fname_ok[PATH_MAX];
+		char cpio_src[(CPIO_HDRLEN + PATH_MAX + 3 + sizeof(fdata)) * 2];
+	} *tbufs = kzalloc_obj(struct test_fname_path_max);
+	struct initramfs_test_cpio c[] = { {
+		.magic = "070701",
+		.ino = 1,
+		.mode = S_IFDIR | 0777,
+		.nlink = 1,
+		.namesize = sizeof(tbufs->fname_oversize),
+		.fname = tbufs->fname_oversize,
+		.filesize = sizeof(fdata),
+		.data = fdata,
+	}, {
+		.magic = "070701",
+		.ino = 2,
+		.mode = S_IFDIR | 0777,
+		.nlink = 1,
+		.namesize = sizeof(tbufs->fname_ok),
+		.fname = tbufs->fname_ok,
+	} };
+
+	memset(tbufs->fname_oversize, '/', sizeof(tbufs->fname_oversize) - 1);
+	memset(tbufs->fname_ok, '/', sizeof(tbufs->fname_ok) - 1);
+	memcpy(tbufs->fname_oversize, "fname_oversize",
+	       sizeof("fname_oversize") - 1);
+	memcpy(tbufs->fname_ok, "fname_ok", sizeof("fname_ok") - 1);
+	len = fill_cpio(c, ARRAY_SIZE(c), false, tbufs->cpio_src);
+
+	/* unpack skips over fname_oversize instead of returning an error */
+	err = unpack_to_rootfs(tbufs->cpio_src, len);
+	KUNIT_EXPECT_NULL(test, err);
+
+	KUNIT_EXPECT_EQ(test, init_stat("fname_oversize", &st0, 0), -ENOENT);
+	KUNIT_EXPECT_EQ(test, init_stat("fname_ok", &st1, 0), 0);
+	KUNIT_EXPECT_EQ(test, init_rmdir("fname_ok"), 0);
+
+	kfree(tbufs);
+}
+
+static void __init initramfs_test_hdr_hex(struct kunit *test)
+{
+	char *err;
+	size_t len;
+	char fdata[] = "this file data will not be unpacked";
+	struct initramfs_test_bufs {
+		char cpio_src[(CPIO_HDRLEN + PATH_MAX + 3 + sizeof(fdata)) * 2];
+	} *tbufs = kzalloc(sizeof(struct initramfs_test_bufs), GFP_KERNEL);
+	struct initramfs_test_cpio c[] = { {
+		.magic = "070701",
+		.ino = 1,
+		.mode = S_IFREG | 0777,
+		.uid = 0x123456,
+		.gid = 0x123457,
+		.nlink = 1,
+		.namesize = sizeof("initramfs_test_hdr_hex_0"),
+		.fname = "initramfs_test_hdr_hex_0",
+		.filesize = sizeof(fdata),
+		.data = fdata,
+	}, {
+		.magic = "070701",
+		.ino = 2,
+		.mode = S_IFDIR | 0777,
+		.uid = 0x000056,
+		.gid = 0x000057,
+		.nlink = 1,
+		.namesize = sizeof("initramfs_test_hdr_hex_1"),
+		.fname = "initramfs_test_hdr_hex_1",
+	} };
+
+	/* inject_ox=true to add "0x" cpio field prefixes */
+	len = fill_cpio(c, ARRAY_SIZE(c), true, tbufs->cpio_src);
+
+	err = unpack_to_rootfs(tbufs->cpio_src, len);
+	KUNIT_EXPECT_NOT_NULL(test, err);
+
+	kfree(tbufs);
+}
+
+/*
+ * The kunit_case/_suite struct cannot be marked as __initdata as this will be
+ * used in debugfs to retrieve results after test has run.
+ */
+static struct kunit_case __refdata initramfs_test_cases[] = {
+	KUNIT_CASE(initramfs_test_extract),
+	KUNIT_CASE(initramfs_test_fname_overrun),
+	KUNIT_CASE(initramfs_test_data),
+	KUNIT_CASE(initramfs_test_csum),
+	KUNIT_CASE(initramfs_test_hardlink),
+	KUNIT_CASE(initramfs_test_many),
+	KUNIT_CASE(initramfs_test_fname_pad),
+	KUNIT_CASE(initramfs_test_fname_path_max),
+	KUNIT_CASE(initramfs_test_hdr_hex),
+	{},
+};
+
+static int __init initramfs_test_init(struct kunit_suite *suite)
+{
+	/*
+	 * unpack_to_rootfs() uses module-static state (victim, byte_count,
+	 * state, ...). The boot-time async do_populate_rootfs() may still be
+	 * running, so wait for it to finish before we call unpack_to_rootfs()
+	 * from the test thread, otherwise the two writers race and crash.
+	 */
+	wait_for_initramfs();
+	return 0;
+}
+
+static struct kunit_suite __refdata initramfs_test_suite = {
+	.name = "initramfs",
+	.suite_init = initramfs_test_init,
+	.test_cases = initramfs_test_cases,
+};
+kunit_test_init_section_suites(&initramfs_test_suite);
+
+MODULE_DESCRIPTION("Initramfs KUnit test suite");
+MODULE_LICENSE("GPL v2");