pNFS: Fix a deadlock when returning a delegation during open()

pNFS: Fix a deadlock when returning a delegation during open()

Ben Coddington reports seeing a hang in the following stack trace:
  0 [ffffd0b50e1774e0] __schedule at ffffffff9ca05415
  1 [ffffd0b50e177548] schedule at ffffffff9ca05717
  2 [ffffd0b50e177558] bit_wait at ffffffff9ca061e1
  3 [ffffd0b50e177568] __wait_on_bit at ffffffff9ca05cfb
  4 [ffffd0b50e1775c8] out_of_line_wait_on_bit at ffffffff9ca05ea5
  5 [ffffd0b50e177618] pnfs_roc at ffffffffc154207b [nfsv4]
  6 [ffffd0b50e1776b8] _nfs4_proc_delegreturn at ffffffffc1506586 [nfsv4]
  7 [ffffd0b50e177788] nfs4_proc_delegreturn at ffffffffc1507480 [nfsv4]
  8 [ffffd0b50e1777f8] nfs_do_return_delegation at ffffffffc1523e41 [nfsv4]
  9 [ffffd0b50e177838] nfs_inode_set_delegation at ffffffffc1524a75 [nfsv4]
 10 [ffffd0b50e177888] nfs4_process_delegation at ffffffffc14f41dd [nfsv4]
 11 [ffffd0b50e1778a0] _nfs4_opendata_to_nfs4_state at ffffffffc1503edf [nfsv4]
 12 [ffffd0b50e1778c0] _nfs4_open_and_get_state at ffffffffc1504e56 [nfsv4]
 13 [ffffd0b50e177978] _nfs4_do_open at ffffffffc15051b8 [nfsv4]
 14 [ffffd0b50e1779f8] nfs4_do_open at ffffffffc150559c [nfsv4]
 15 [ffffd0b50e177a80] nfs4_atomic_open at ffffffffc15057fb [nfsv4]
 16 [ffffd0b50e177ad0] nfs4_file_open at ffffffffc15219be [nfsv4]
 17 [ffffd0b50e177b78] do_dentry_open at ffffffff9c09e6ea
 18 [ffffd0b50e177ba8] vfs_open at ffffffff9c0a082e
 19 [ffffd0b50e177bd0] dentry_open at ffffffff9c0a0935

The issue is that the delegreturn is being asked to wait for a layout
return that cannot complete because a state recovery was initiated. The
state recovery cannot complete until the open() finishes processing the
delegations it was given.

The solution is to propagate the existing flags that indicate a
non-blocking call to the function pnfs_roc(), so that it knows not to
wait in this situation.

Reported-by: Benjamin Coddington <bcodding@hammerspace.com>
Fixes: 29ade5db1293 ("pNFS: Wait on outstanding layoutreturns to complete in pnfs_roc()")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>