[PATCH 4.19 08/58] dm: avoid filesystem lookup in dm_get_dev_t()

Greg Kroah-Hartman
2021-01-26T16:39:19Z

From: Hannes Reinecke <hare@suse.de>

commit 809b1e4945774c9ec5619a8f4e2189b7b3833c0c upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/dm-table.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -431,14 +431,23 @@ int dm_get_device(struct dm_target *ti,
{
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) {