[PATCH V5 0/4] btrf_show_devname related fixes

[Anand Jain <anand.jain@oracle.com>]

v5: Patches reorged.
 Patch (btrfs: consolidate device_list_mutex in prepare_sprout to its parent)
 moved into a new set as it has a dependency on an older patch in the ML.
 Change log updated.
v4: Fix unrelated changes
v3: Add missing rcu_lock in show_devname
v2: Use latest_dev so that device path is also shown

Su Yue reported [1] warn() as a result of a race between the following two
threads,
  Thread-A: function stack leading to btrfs_prepare_sprout()
and
  Thread-B: function stack leading to btrfs_show_devname()

[1]  https://patchwork.kernel.org/project/linux-btrfs/patch/20210818041944.5793-1-l@damenly.su/

While btrfs_prepare_sprout() moves the fs_devices::devices into
fs_devices::seed_list, the btrfs_show_devname searched for the devices
and found none, leading to the warning as in [1] (above).

The btrfs_prepare_sprout() uses device_list_mutex however
btrfs_show_devname() don't and, the device_list_mutex in
btrfs_show_devname() was removed by the patch 88c14590cdd6
(btrfs: use RCU in btrfs_show_devname for device list traversal)
for the perforamcne reasons.

This series does not intend to reintroduce the device_list_mutex in
btrfs_prepare_sprout() but instead saves the pointer to btrfs_devices
in the fs_devices::latest_dev so that btrfs_show_devname() can use it.

patch 1 converts fs_devices::latest_bdev type from struct block_device to
        struct btrfs_device and renames it to latest_dev
patch 2 btrfs_show_devname() uses the fs_devices::latest_dev::name to show
        the device path in the /proc/self/mounts
patch 3 fixes a stale latest_dev pointer after the sprout operation
patch 4 fixes an old comment about the function btrfs_show_devname()

Anand Jain (4):
  btrfs: convert latest_bdev type to struct btrfs_device and rename
  btrfs: use latest_dev in btrfs_show_devname
  btrfs: update latest_dev when we sprout
  btrfs: fix comment about the btrfs_show_devname

 fs/btrfs/disk-io.c   |  6 +++---
 fs/btrfs/extent_io.c |  2 +-
 fs/btrfs/inode.c     |  2 +-
 fs/btrfs/super.c     | 26 ++++----------------------
 fs/btrfs/volumes.c   | 17 ++++++++---------
 fs/btrfs/volumes.h   |  2 +-
 6 files changed, 18 insertions(+), 37 deletions(-)

-- 
2.31.1