dm: avoid filesystem lookup in dm_get_dev_t()

This reverts commit
644bda6f3460 ("dm table: fall back to getting device using name_to_dev_t()")

dm_get_dev_t() is just used to convert an arbitrary 'path' string
into a dev_t. It doesn't presume that the device is present; that
check will be done later, as the only caller is dm_get_device(),
which does a dm_get_table_device() later on, which will properly
open the device.

So if the path string already _is_ in major:minor representation
we can convert it directly, avoiding a recursion into the filesystem
to lookup the block device.

This avoids a hang in multipath_message() when the filesystem is
inaccessible.

Fixes: 644bda6f3460 ("dm table: fall back to getting device using name_to_dev_t()")
Cc: stable@vger.kernel.org
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin Wilck <mwilck@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 188f412..4acf234 100644 (file)
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -363,14 +363,23 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
 {
        int r;
        dev_t dev;
+       unsigned int major, minor;
+       char dummy;
        struct dm_dev_internal *dd;
        struct dm_table *t = ti->table;
 
        BUG_ON(!t);
 
-       dev = dm_get_dev_t(path);
-       if (!dev)
-               return -ENODEV;
+       if (sscanf(path, "%u:%u%c", &major, &minor, &dummy) == 2) {
+               /* Extract the major/minor numbers */
+               dev = MKDEV(major, minor);
+               if (MAJOR(dev) != major || MINOR(dev) != minor)
+                       return -EOVERFLOW;
+       } else {
+               dev = dm_get_dev_t(path);
+               if (!dev)
+                       return -ENODEV;
+       }
 
        dd = find_device(&t->devices, dev);
        if (!dd) {