tracing: fprobe: Fix RCU warning message in list traversal

When CONFIG_PROVE_RCU_LIST is enabled, fprobe triggers the following
warning:

    WARNING: suspicious RCU usage
    kernel/trace/fprobe.c:457 RCU-list traversed in non-reader section!!

    other info that might help us debug this:
	#1: ffffffff863c4e08 (fprobe_mutex){+.+.}-{4:4}, at: fprobe_module_callback+0x7b/0x8c0

    Call Trace:
	fprobe_module_callback
	notifier_call_chain
	blocking_notifier_call_chain

This warning occurs because fprobe_remove_node_in_module() traverses an
RCU list using RCU primitives without holding an RCU read lock. However,
the function is only called from fprobe_module_callback(), which holds
the fprobe_mutex lock that provides sufficient protection for safely
traversing the list.

Fix the warning by specifying the locking design to the
CONFIG_PROVE_RCU_LIST mechanism. Add the lockdep_is_held() argument to
hlist_for_each_entry_rcu() to inform the RCU checker that fprobe_mutex
provides the required protection.

Link: https://lore.kernel.org/all/20250410-fprobe-v1-1-068ef5f41436@debian.org/
Fixes: a3dc2983ca7b90 ("tracing: fprobe: Cleanup fprobe hash when module unloading")
Signed-off-by: Breno Leitao <leitao@debian.org>
Tested-by: Antonio Quartulli <antonio@mandelbit.com>
Tested-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 95c6e3473a76b516047768c2a0f7edb6df636851..ba7ff14f5339b5ea41f50ccde887f0a1bd4b6aab 100644 (file)
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -454,7 +454,8 @@ static void fprobe_remove_node_in_module(struct module *mod, struct hlist_head *
        struct fprobe_hlist_node *node;
        int ret = 0;
 
-       hlist_for_each_entry_rcu(node, head, hlist) {
+       hlist_for_each_entry_rcu(node, head, hlist,
+                                lockdep_is_held(&fprobe_mutex)) {
                if (!within_module(node->addr, mod))
                        continue;
                if (delete_fprobe_node(node))