On Wed, Oct 09, 2019 at 11:19:16PM -0700, Song Liu wrote: > bpf stackmap with build-id lookup (BPF_F_STACK_BUILD_ID) can trigger A-A > deadlock on rq_lock(): > > rcu: INFO: rcu_sched detected stalls on CPUs/tasks: > [...] > Call Trace: > try_to_wake_up+0x1ad/0x590 > wake_up_q+0x54/0x80 > rwsem_wake+0x8a/0xb0 > bpf_get_stack+0x13c/0x150 > bpf_prog_fbdaf42eded9fe46_on_event+0x5e3/0x1000 > bpf_overflow_handler+0x60/0x100 > __perf_event_overflow+0x4f/0xf0 > perf_swevent_overflow+0x99/0xc0 > ___perf_sw_event+0xe7/0x120 > __schedule+0x47d/0x620 > schedule+0x29/0x90 > futex_wait_queue_me+0xb9/0x110 > futex_wait+0x139/0x230 > do_futex+0x2ac/0xa50 > __x64_sys_futex+0x13c/0x180 > do_syscall_64+0x42/0x100 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 >
> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c > index 052580c33d26..3b278f6b0c3e 100644 > --- a/kernel/bpf/stackmap.c > +++ b/kernel/bpf/stackmap.c > @@ -287,7 +287,7 @@ static void stack_map_get_build_id_offset(struct > bpf_stack_build_id *id_offs, > bool irq_work_busy = false; > struct stack_map_irq_work *work = NULL; > > - if (in_nmi()) { > + if (in_nmi() || this_rq_is_locked()) { > work = this_cpu_ptr(&up_read_work); > if (work->irq_work.flags & IRQ_WORK_BUSY) > /* cannot queue more up_read, fallback */ This is horrific crap. Just say no to that get_build_id_offset() trainwreck.