On 10/10/19 12:36 AM, Peter Zijlstra wrote:
> 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.
this is not a helpful comment.
What issues do you see with this approach?
