Subject: Re: [PATCH] bpf: convert hashtab lock to raw lock

From: Alexei Starovoitov <[email-masked]>
Date: Fri, 30 Oct 2015 17:03:58 -0700

On Fri, Oct 30, 2015 at 03:16:26PM -0700, Yang Shi wrote:
> When running bpf samples on rt kernel, it reports the below warning:
> 
> BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:917
> in_atomic(): 1, irqs_disabled(): 128, pid: 477, name: ping
> Preemption disabled at:[<ffff80000017db58>] kprobe_perf_func+0x30/0x228
...
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index 83c209d..972b76b 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -17,7 +17,7 @@
>  struct bpf_htab {
>  	struct bpf_map map;
>  	struct hlist_head *buckets;
> -	spinlock_t lock;
> +	raw_spinlock_t lock;

How do we address such things in general?
I bet there are tons of places around the kernel that
call spin_lock from atomic.
I'd hate to lose the benefits of lockdep of non-raw spin_lock
just to make rt happy.