init: Add support for rootwait timeout parameter

Add an optional timeout arg to 'rootwait' as the maximum time in
seconds to wait for the root device to show up before attempting
forced mount of the root filesystem.

Use case:
In case of device mapper usage for the rootfs (e.g. root=/dev/dm-0),
if the mapper is not able to create the virtual block for any reason
(wrong arguments, bad dm-verity signature, etc), the `rootwait` param
causes the kernel to wait forever. It may however be desirable to only
wait for a given time and then panic (force mount) to cause device reset.
This gives the bootloader a chance to detect the problem and to take some
measures, such as marking the booted partition as bad (for A/B case) or
entering a recovery mode.

In success case, mounting happens as soon as the root device is ready,
unlike the existing 'rootdelay' parameter which performs an unconditional
pause.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Message-Id: <20230813082349.513386-1-loic.poulain@linaro.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 36 insertions, 2 deletions

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 1aa015883519..5dfd30b13f48 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/ramfs.h>
 #include <linux/shmem_fs.h>
+#include <linux/ktime.h>
 
 #include <linux/nfs_fs.h>
 #include <linux/nfs_fs_sb.h>
@@ -71,12 +72,37 @@ static int __init rootwait_setup(char *str)
 {
 	if (*str)
 		return 0;
-	root_wait = 1;
+	root_wait = -1;
 	return 1;
 }
 
 __setup("rootwait", rootwait_setup);
 
+static int __init rootwait_timeout_setup(char *str)
+{
+	int sec;
+
+	if (kstrtoint(str, 0, &sec) || sec < 0) {
+		pr_warn("ignoring invalid rootwait value\n");
+		goto ignore;
+	}
+
+	if (check_mul_overflow(sec, MSEC_PER_SEC, &root_wait)) {
+		pr_warn("ignoring excessive rootwait value\n");
+		goto ignore;
+	}
+
+	return 1;
+
+ignore:
+	/* Fallback to indefinite wait */
+	root_wait = -1;
+
+	return 1;
+}
+
+__setup("rootwait=", rootwait_timeout_setup);
+
 static char * __initdata root_mount_data;
 static int __init root_data_setup(char *str)
 {
@@ -384,14 +410,22 @@ void __init mount_root(char *root_device_name)
 /* wait for any asynchronous scanning to complete */
 static void __init wait_for_root(char *root_device_name)
 {
+	ktime_t end;
+
 	if (ROOT_DEV != 0)
 		return;
 
 	pr_info("Waiting for root device %s...\n", root_device_name);
 
+	end = ktime_add_ms(ktime_get_raw(), root_wait);
+
 	while (!driver_probe_done() ||
-	       early_lookup_bdev(root_device_name, &ROOT_DEV) < 0)
+	       early_lookup_bdev(root_device_name, &ROOT_DEV) < 0) {
 		msleep(5);
+		if (root_wait > 0 && ktime_after(ktime_get_raw(), end))
+			break;
+	}
+
 	async_synchronize_full();
 
 }