Hi,
On 2/25/2025 6:16 AM, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@xxxxxxxxxx>
>
> Fix the following deadlock:
> CPU A
> _free_event()
> perf_kprobe_destroy()
> mutex_lock(&event_mutex)
> perf_trace_event_unreg()
> synchronize_rcu_tasks_trace()
>
> There are several paths where _free_event() grabs event_mutex
> and calls sync_rcu_tasks_trace. Above is one such case.
>
> CPU B
> bpf_prog_test_run_syscall()
> rcu_read_lock_trace()
> bpf_prog_run_pin_on_cpu()
> bpf_prog_load()
> bpf_tracing_func_proto()
> trace_set_clr_event()
> mutex_lock(&event_mutex)
Considering the unregistered case is not so frequency, would it better
to use mutex_trylock firstly, then fallback to workqueue when the
event_mutex is busy ?
>
> Delegate trace_set_clr_event() to workqueue to avoid
> such lock dependency.
>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> ---
> kernel/trace/bpf_trace.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index a612f6f182e5..13bef2462e94 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -392,7 +392,7 @@ static const struct bpf_func_proto bpf_trace_printk_proto = {
> .arg2_type = ARG_CONST_SIZE,
> };
>
> -static void __set_printk_clr_event(void)
> +static void __set_printk_clr_event(struct work_struct *work)
> {
> /*
> * This program might be calling bpf_trace_printk,
> @@ -405,10 +405,11 @@ static void __set_printk_clr_event(void)
> if (trace_set_clr_event("bpf_trace", "bpf_trace_printk", 1))
> pr_warn_ratelimited("could not enable bpf_trace_printk events");
> }
> +static DECLARE_WORK(set_printk_work, __set_printk_clr_event);
>
> const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
> {
> - __set_printk_clr_event();
> + schedule_work(&set_printk_work);
> return &bpf_trace_printk_proto;
> }
>
> @@ -451,7 +452,7 @@ static const struct bpf_func_proto bpf_trace_vprintk_proto = {
>
> const struct bpf_func_proto *bpf_get_trace_vprintk_proto(void)
> {
> - __set_printk_clr_event();
> + schedule_work(&set_printk_work);
> return &bpf_trace_vprintk_proto;
> }
>
