Re: [PATCH V5 0/4] btrf_show_devname related fixes

[Su Yue <l@damenly.su>]

On Tue 24 Aug 2021 at 13:05, Anand Jain <anand.jain@oracle.com> 
wrote:

> 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
>

For patch [123], you can add

Tested-by: Su Yue <l@damenly.su>

Thanks.
--
Su
> 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(-)