bpf: Fix deadlock between rcu_tasks_trace and event_mutex.

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)

Delegate trace_set_clr_event() to workqueue to avoid
such lock dependency.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250224221637.4780-1-alexei.starovoitov@gmail.com

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index a612f6f182e511c6ccaf29b726bea32a9c722936..13bef2462e94b008a90e4d34b8824add336fbf43 100644 (file)
--- 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;
 }