Re: [PATCH v2] kernel: bpf: stackmap: fix a possible sleep-in-atomic bug in bpf_mmap_unlock_get_irq_work()

[Alexei Starovoitov]

On Fri, Mar 17, 2023 at 03:52:27AM +0000, starmiku1207184332@xxxxxxxxx wrote:
> context because of its possible sleep operation. However, mmap_read_unlock()
> is unsafely called in a preempt disabled context when spin_lock() or
> rcu_read_lock() has been called.

Why is that unsafe?
See __up_read(). It's doing preempt_disable().


> -	if (irqs_disabled()) {
> +	if (in_atomic() || irqs_disabled()) {

We cannot do this. It will significantly hurt stack traces with build_id.