mm/swapfile: do not sleep with a spin lock held

We can't call kvfree() with a spin lock held, so defer it.  Fixes a
might_sleep() runtime warning.

Fixes: 873d7bcf ("mm/swapfile.c: use kvzalloc for swap_info_struct allocation")
Signed-off-by: Qian Cai <qcai@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201202151549.10350-1-qcai@redhat.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>