netdev - [PATCH v2 09/13] notifier: Show function names on notifier routines if DEBUG

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Date:   Tue, 19 Jul 2022 16:53:22 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     akpm@...ux-foundation.org, bhe@...hat.com, pmladek@...e.com,
        kexec@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        netdev@...r.kernel.org, x86@...nel.org, kernel-dev@...lia.com,
        kernel@...ccoli.net, halves@...onical.com, fabiomirmar@...il.com,
        alejandro.j.jimenez@...cle.com, andriy.shevchenko@...ux.intel.com,
        arnd@...db.de, bp@...en8.de, corbet@....net,
        d.hatayama@...fujitsu.com, dave.hansen@...ux.intel.com,
        dyoung@...hat.com, feng.tang@...el.com, gregkh@...uxfoundation.org,
        mikelley@...rosoft.com, hidehiro.kawai.ez@...achi.com,
        jgross@...e.com, john.ogness@...utronix.de, keescook@...omium.org,
        luto@...nel.org, mhiramat@...nel.org, mingo@...hat.com,
        paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, stern@...land.harvard.edu,
        tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com,
        will@...nel.org, "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Xiaoming Ni <nixiaoming@...wei.com>
Subject: [PATCH v2 09/13] notifier: Show function names on notifier routines if DEBUG_NOTIFIERS is set

Currently we have a debug infrastructure in the notifiers file, but
it's very simple/limited. Extend it by:

(a) Showing all registered/unregistered notifiers' callback names;

(b) Adding a dynamic debug tuning to allow showing called notifiers'
function names. Notice that this should be guarded as a tunable since
it can flood the kernel log buffer.

Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Valentin Schneider <valentin.schneider@....com>
Cc: Xiaoming Ni <nixiaoming@...wei.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>

---

V2:
- Major improvement thanks to the great idea from Xiaoming - changed
all the ksym wheel reinvention to printk %ps modifier;

- Instead of ifdefs, using IS_ENABLED() - thanks Steven.

- Removed an unlikely() hint on debug path.

 kernel/notifier.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/kernel/notifier.c b/kernel/notifier.c
index 0d5bd62c480e..350761b34f8a 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -37,6 +37,10 @@ static int notifier_chain_register(struct notifier_block **nl,
 	}
 	n->next = *nl;
 	rcu_assign_pointer(*nl, n);
+
+	if (IS_ENABLED(CONFIG_DEBUG_NOTIFIERS))
+		pr_info("notifiers: registered %ps\n", n->notifier_call);
+
 	return 0;
 }
 
@@ -46,6 +50,11 @@ static int notifier_chain_unregister(struct notifier_block **nl,
 	while ((*nl) != NULL) {
 		if ((*nl) == n) {
 			rcu_assign_pointer(*nl, n->next);
+
+			if (IS_ENABLED(CONFIG_DEBUG_NOTIFIERS))
+				pr_info("notifiers: unregistered %ps\n",
+					n->notifier_call);
+
 			return 0;
 		}
 		nl = &((*nl)->next);
@@ -77,13 +86,14 @@ static int notifier_call_chain(struct notifier_block **nl,
 	while (nb && nr_to_call) {
 		next_nb = rcu_dereference_raw(nb->next);
 
-#ifdef CONFIG_DEBUG_NOTIFIERS
-		if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
-			WARN(1, "Invalid notifier called!");
-			nb = next_nb;
-			continue;
+		if (IS_ENABLED(CONFIG_DEBUG_NOTIFIERS)) {
+			if (!func_ptr_is_kernel_text(nb->notifier_call)) {
+				WARN(1, "Invalid notifier called!");
+				nb = next_nb;
+				continue;
+			}
+			pr_debug("notifiers: calling %ps\n", nb->notifier_call);
 		}
-#endif
 		ret = nb->notifier_call(nb, val, v);
 
 		if (nr_calls)
-- 
2.37.1