ceph: fix pending vmtruncate race

The locking order for pending vmtruncate is wrong, it can lead to
following race:

        write                  wmtruncate work
------------------------    ----------------------
lock i_mutex
check i_truncate_pending   check i_truncate_pending
truncate_inode_pages()     lock i_mutex (blocked)
copy data to page cache
unlock i_mutex
                           truncate_inode_pages()

The fix is take i_mutex before calling __ceph_do_pending_vmtruncate()

Fixes: http://tracker.ceph.com/issues/5453
Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Sage Weil <sage@inktank.com>
ceph: fix cap revoke race

If caps are been revoking by the auth MDS, don't consider them as
issued even they are still issued by non-auth MDS. The non-auth
MDS should also be revoking/exporting these caps, the client just
hasn't received the cap revoke/export message.

The race I encountered is: When caps are exporting to new MDS, the
client receives cap import message and cap revoke message from the
new MDS, then receives cap export message from the old MDS. When
the client receives cap revoke message from the new MDS, the revoking
caps are still issued by the old MDS, so the client does nothing.
Later when the cap export message is received, the client removes
the caps issued by the old MDS. (Another way to fix the race is
calling ceph_check_caps() in handle_cap_export())

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Sage Weil <sage@inktank.com>
ceph: fix race between cap issue and revoke

If we receive new caps from the auth MDS and the non-auth MDS is
revoking the newly issued caps, we should release the caps from
the non-auth MDS. The scenario is filelock's state changes from
SYNC to LOCK. Non-auth MDS revokes Fc cap, the client gets Fc cap
from the auth MDS at the same time.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Sage Weil <sage@inktank.com>
possible btrfs fix from chris