commit 7c542a5a027caa95bb00f8a8223c7e4aef88c931
Author: Pierre Ossman <drzeus@drzeus.cx>
Date:   Mon May 14 14:15:46 2007 +0200

    init: wait for asynchronously scanned block devices
    
    Some buses (e.g. USB and MMC) do their scanning of devices in the
    background, causing a race between them and prepare_namespace().
    In order to be able to use these buses without an initrd, we now
    wait for the device specified in root= to actually show up.
    
    If the device never shows up than we will hang in an infinite loop.
    Previously we panic:ed instead, so this behaviour should be no
    worse.
    
    Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 46fe407..192b2d6 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -438,11 +438,24 @@ void __init prepare_namespace(void)
 			root_device_name += 5;
 	}
 
-	is_floppy = MAJOR(ROOT_DEV) == FLOPPY_MAJOR;
-
 	if (initrd_load())
 		goto out;
 
+	/* wait for any asynchronous scanning to complete */
+	if (ROOT_DEV == 0) {
+		printk("Waiting for root device %s...\n", saved_root_name);
+		do {
+			while (driver_probe_done() != 0)
+				msleep(100);
+			ROOT_DEV = name_to_dev_t(saved_root_name);
+			if (ROOT_DEV == 0)
+				msleep(100);
+		} while (ROOT_DEV == 0);
+	}
+
+	is_floppy = MAJOR(ROOT_DEV) == FLOPPY_MAJOR;
+
+
 	if (is_floppy && rd_doload && rd_load_disk(0))
 		ROOT_DEV = Root_RAM0;