initramfs_test: use test init/exit hooks to override init fs

Most initramfs kunit tests interact with initramfs via
unpack_to_rootfs() and subsequently init_stat(), init_unlink(), etc.

It's cleaner and less error-prone to override current->fs with
userspace_init_fs for all initramfs_test_suite tests.

Link: https://patch.msgid.link/20260701-work-kunit-nullfs-v1-1-dfa60270434f@kernel.org
Link: https://patch.msgid.link/20260729151320.21001-2-ddiss@suse.de
Fixes: 32750c77e811 ("fs: start all kthreads in nullfs")
Reported-by: Mark Brown <broonie@kernel.org>
Closes: https://lore.kernel.org/r/akOrbOsKUqgZarGw@sirena.org.uk
Signed-off-by: David Disseldorp <ddiss@suse.de>
Co-developed-by: David Disseldorp <ddiss@suse.de>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

diff --git a/drivers/char/misc_minor_kunit.c b/drivers/char/misc_minor_kunit.c
index e930c78e1ef97eafaee5892413bb3a29e4b147ad..e85210cbb6401d3dce9603ea9c6c67226617d071 100644 (file)
--- a/drivers/char/misc_minor_kunit.c
+++ b/drivers/char/misc_minor_kunit.c
@@ -5,6 +5,7 @@
 #include <linux/miscdevice.h>
 #include <linux/fs.h>
 #include <linux/file.h>
+#include <linux/fs_struct.h>
 #include <linux/init_syscalls.h>
 
 /* static minor (LCD_MINOR) */
@@ -160,18 +161,22 @@ static void __init miscdev_test_can_open(struct kunit *test, struct miscdevice *
        char *devname;
 
        devname = kasprintf(GFP_KERNEL, "/dev/%s", misc->name);
-       ret = init_mknod(devname, S_IFCHR | 0600,
-                        new_encode_dev(MKDEV(MISC_MAJOR, misc->minor)));
-       if (ret != 0)
-               KUNIT_FAIL(test, "failed to create node\n");
 
-       filp = filp_open(devname, O_RDONLY, 0);
-       if (IS_ERR(filp))
-               KUNIT_FAIL(test, "failed to open misc device: %ld\n", PTR_ERR(filp));
-       else
-               fput(filp);
+       /* Tests run in a nullfs kthread; borrow the init fs to resolve /dev. */
+       scoped_with_init_fs() {
+               ret = init_mknod(devname, S_IFCHR | 0600,
+                                new_encode_dev(MKDEV(MISC_MAJOR, misc->minor)));
+               if (ret != 0)
+                       KUNIT_FAIL(test, "failed to create node\n");
+
+               filp = filp_open(devname, O_RDONLY, 0);
+               if (IS_ERR(filp))
+                       KUNIT_FAIL(test, "failed to open misc device: %ld\n", PTR_ERR(filp));
+               else
+                       fput(filp);
 
-       init_unlink(devname);
+               init_unlink(devname);
+       }
        kfree(devname);
 }
 

diff --git a/init/initramfs_test.c b/init/initramfs_test.c
index bc55306d226dc0c5197878311f77fc9378a5b02f..9cf316c13ffa5c8850f9cceba4516c8e490bbeda 100644 (file)
--- a/init/initramfs_test.c
+++ b/init/initramfs_test.c
@@ -3,6 +3,7 @@
 #include <linux/fcntl.h>
 #include <linux/file.h>
 #include <linux/fs.h>
+#include <linux/fs_struct.h>
 #include <linux/init.h>
 #include <linux/init_syscalls.h>
 #include <linux/initrd.h>
@@ -562,7 +563,7 @@ static struct kunit_case __refdata initramfs_test_cases[] = {
        {},
 };
 
-static int __init initramfs_test_init(struct kunit_suite *suite)
+static int __init initramfs_suite_init(struct kunit_suite *suite)
 {
        /*
         * unpack_to_rootfs() uses module-static state (victim, byte_count,
@@ -574,9 +575,23 @@ static int __init initramfs_test_init(struct kunit_suite *suite)
        return 0;
 }
 
+/* Tests run in a nullfs kthread; always use the init fs for path resolution. */
+static int __init initramfs_test_init(struct kunit *test)
+{
+       test->priv = __override_init_fs();
+       return 0;
+}
+
+static void __init initramfs_test_exit(struct kunit *test)
+{
+       __revert_init_fs(test->priv);
+}
+
 static struct kunit_suite __refdata initramfs_test_suite = {
        .name = "initramfs",
-       .suite_init = initramfs_test_init,
+       .suite_init = initramfs_suite_init,
+       .init = initramfs_test_init,
+       .exit = initramfs_test_exit,
        .test_cases = initramfs_test_cases,
 };
 kunit_test_init_section_suites(&initramfs_test_suite);