raw_spin_lock(): unexpected null pointer exception - linux-kernel

Question

So I adapted some of the /kernel/sched/rt.c code to write my own simple CPU scheduler, and I'm getting a null pointer dereference exception when I try to acquire a lock. This is despite me printk()'ing all of the relevant pointers, and seeing that they're not NULL.
//Snippet from my adaptation of update_curr_rt()
//wrr_rq is a struct wrr_rq*
printk("Before loop, wrr_rq pointer is %p\n",wrr_rq);
printk("Before loop, &wrr_rq->wrr_runtime_lock is %p\n",&wrr_rq->wrr_runtime_lock);
for_each_sched_wrr_entity(wrr_se) {
printk("1\n");
wrr_rq = wrr_rq_of_se(wrr_se);
printk("2\n");
raw_spin_lock(&wrr_rq->wrr_runtime_lock);
printk("3\n");
[ 263.595176] Before loop, wrr_rq is 00000000aebb4d6d
[ 263.596283] Before loop, &wrr_rq->wrr_runtime_lock is 0000000015dee87f
[ 263.597764] 1
[ 263.598141] wrr_rq_of_se: called
[ 263.598888] 2
[ 263.599268] BUG: kernel NULL pointer dereference, address: 0000000000000068
[ 263.600836] #PF: supervisor write access in kernel mode
[ 263.602027] #PF: error_code(0x0002) - not-present page
...
[ 263.656134] RIP: 0010:_raw_spin_lock+0x7/0x20
I've printed all the relevant pointers and seen they're not NULL (and have values quite a bit above 0), but I still get this exception. I tried using the elixir browser to see what is happening with the raw_spin_lock() macro, and it doesn't seem like anything crazy is happening...
In addition, the runqueue lock is already held when this code is called (the runqueue lock is acquired by task_sched_runtime()).
Any thoughts appreciated.
Thanks.

Answer 1

Credit to #0andriy: It turns out that kernel NULL pointers when printed by %p get hashed to some other unique value that may not be NULL, and so when I printed things with %px I saw they were in fact NULL.