uml: handle block device hotplug errors

If a disk fails to open, i.e.  its host file doesn't exist, it won't be
removable because the hot-unplug code checks the existence of its gendisk.
This won't exist because it is only allocated for successfully opened disks.
Thus, a typo on the command line can result in a unusable and unfixable disk.

This is fixed by freeing the gendisk if it's there, but not letting that
affect the removal.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 6 deletions

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 8bd9204ac1ab..53c36d1770c5 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -788,14 +788,12 @@ static int ubd_id(char **str, int *start_out, int *end_out)
 
 static int ubd_remove(int n, char **error_out)
 {
+        struct gendisk *disk;
         struct ubd *ubd_dev;
         int err = -ENODEV;
 
         mutex_lock(&ubd_lock);
 
-        if(ubd_gendisk[n] == NULL)
-                goto out;
-
         ubd_dev = &ubd_devs[n];
 
         if(ubd_dev->file == NULL)
@@ -806,9 +804,12 @@ static int ubd_remove(int n, char **error_out)
         if(ubd_dev->count > 0)
                 goto out;
 
-        del_gendisk(ubd_gendisk[n]);
-        put_disk(ubd_gendisk[n]);
-        ubd_gendisk[n] = NULL;
+        disk = ubd_gendisk[n];
+        ubd_gendisk[n] = NULL;
+        if(disk != NULL){
+                del_gendisk(disk);
+                put_disk(disk);
+        }
 
         if(fake_gendisk[n] != NULL){
                 del_gendisk(fake_gendisk[n]);