Re: [PATCH v2 bpf-next] bpf/stackmap: fix deadlock with rq_lock in bpf_get_stack()

[Alexei Starovoitov]

On Mon, Oct 14, 2019 at 10:12 AM Song Liu <songliubraving@xxxxxx> 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
>
> This can be reproduced by:
> 1. Start a multi-thread program that does parallel mmap() and malloc();
> 2. taskset the program to 2 CPUs;
> 3. Attach bpf program to trace_sched_switch and gather stackmap with
>    build-id, e.g. with trace.py from bcc tools:
>    trace.py -U -p <pid> -s <some-bin,some-lib> t:sched:sched_switch
>
> A sample reproducer is attached at the end.
>
> This could also trigger deadlock with other locks that are nested with
> rq_lock.
>
> Fix this by checking whether irqs are disabled. Since rq_lock and all
> other nested locks are irq safe, it is safe to do up_read() when irqs are
> not disable. If the irqs are disabled, postpone up_read() in irq_work.
>
> Fixes: commit 615755a77b24 ("bpf: extend stackmap to save binary_build_id+offset instead of address")
> Cc: stable@xxxxxxxxxxxxxxx # v4.17+
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Signed-off-by: Song Liu <songliubraving@xxxxxx>

I fixed 'Fixes' tag and applied to bpf-next.
Thanks