Re: [PATCH 0/6 v6] NFSD: Pin to vfsmount for nfsd exports cache

[Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Sorry for the bad title of v6, it should be v5.

Please ignore the threads of v6.

On 6/17/2015 3:44 PM, Kinglong Mee wrote:
> If there are some mount points(not exported for nfs) under pseudo root,
> after client's operation of those entry under the root, anyone *can't*
> unmount those mount points until export cache expired.
> 
> # cat /etc/exports
> /nfs/xfs        *(rw,insecure,no_subtree_check,no_root_squash)
> /nfs/pnfs       *(rw,insecure,no_subtree_check,no_root_squash)
> # ll /nfs/
> total 0
> drwxr-xr-x. 3 root root 84 Apr 21 22:27 pnfs
> drwxr-xr-x. 3 root root 84 Apr 21 22:27 test
> drwxr-xr-x. 2 root root  6 Apr 20 22:01 xfs
> # mount /dev/sde /nfs/test
> # df
> Filesystem                      1K-blocks    Used Available Use% Mounted on
> ......
> /dev/sdd                          1038336   32944   1005392   4% /nfs/pnfs
> /dev/sdc                         10475520   32928  10442592   1% /nfs/xfs
> /dev/sde                           999320    1284    929224   1% /nfs/test
> # mount -t nfs 127.0.0.1:/nfs/ /mnt
> # ll /mnt/*/
> /mnt/pnfs/:
> total 0
> -rw-r--r--. 1 root root 0 Apr 21 22:23 attr
> drwxr-xr-x. 2 root root 6 Apr 21 22:19 tmp
> 
> /mnt/xfs/:
> total 0
> # umount /nfs/test/
> umount: /nfs/test/: target is busy
>         (In some cases useful info about processes that
>          use the device is found by lsof(8) or fuser(1).)
> 
> It's caused by exports cache of nfsd holds the reference of
> the path (here is /nfs/test/), so, it can't be umounted.
> 
> I don't think that's user expect, they want umount /nfs/test/.
> Bruce think user can also umount /nfs/pnfs/ and /nfs/xfs.
> 
> This patch site lets nfsd exports pinning to vfsmount, 
> not using mntget, so user can umount any exports mountpoint now.
> 
> v3, 
> 1. New helpers path_get_pin/path_put_unpin for path pin.
> 2. Use kzalloc for allocating memory.
> 
> v4, Thanks for Al Viro's commets for the logic of fs_pin.
> 1. add a completion for pin_kill waiting the reference is decreased to zero.
> 2. add a work_struct for pin_kill decreases the reference indirectly.
> 3. free svc_export/svc_expkey in pin_kill, not svc_export_put/svc_expkey_put.
> 4. svc_export_put/svc_expkey_put go though pin_kill logic.
> 
> v5, 
> let killing fs_pin under a reference of vfsmnt.
> 
> Kinglong Mee (6):
>   fs_pin: Initialize value for fs_pin explicitly
>   fs_pin: Export functions for specific filesystem
>   fs_pin: Kill fs_pin under a reference of vfsmnt
>   path: New helpers path_get_pin/path_put_unpin for path pin
>   sunrpc: New helper cache_force_expire for cache cleanup
>   nfsd: Allows user un-mounting filesystem where nfsd exports base on
> 
>  fs/fs_pin.c                  |  4 ++
>  fs/namei.c                   | 26 ++++++++++++
>  fs/namespace.c               | 10 ++++-
>  fs/nfsd/export.c             | 96 +++++++++++++++++++++++++++++++++++---------
>  fs/nfsd/export.h             | 18 ++++++++-
>  include/linux/fs_pin.h       |  6 +++
>  include/linux/path.h         |  4 ++
>  include/linux/sunrpc/cache.h | 11 +++++
>  8 files changed, 154 insertions(+), 21 deletions(-)
> 
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