[PATCH AUTOSEL 6.1 05/10] bpf: Fix deadlock between rcu_tasks_trace and event_mutex.

[PATCH AUTOSEL 6.1 05/10] bpf: Fix deadlock between rcu_tasks_trace and event_mutex.

[Sasha Levin]

From: Alexei Starovoitov <ast@kernel.org>

[ Upstream commit 4580f4e0ebdf8dc8d506ae926b88510395a0c1d1 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 af48f66466e81..91d0d1cce09b3 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -403,7 +403,7 @@ 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,
@@ -416,10 +416,11 @@ 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;
 }
 
@@ -462,7 +463,7 @@ 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;
 }
 
-- 
2.39.5