At least out_of_memory() calls has_intersects_mems_allowed() without
even rcu_read_lock(), this is obviously buggy.
Add the necessary rcu_read_lock(). This means that we can not simply
return from the loop, we need "bool ret" and "break".
While at it, swap the names of task_struct's (the argument and the
local). This cleans up the code a little bit and avoids the unnecessary
initialization.