i_dir_seq is subject to concurrent modification by a cmpxchg or
store-release operation, so ensure that the relaxed access in
d_alloc_parallel uses READ_ONCE.
Reported-by: NPeter Zijlstra <peterz@infradead.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>