Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Vasily Averin <vvs@virtuozzo.com>
Subject: [PATCH] notifiers: double register detection
To:     linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
Message-ID: <04127e71-4782-9bbb-fe5a-7c01e93a99b0@virtuozzo.com>
Date:   Tue, 12 Mar 2019 11:06:32 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.4.0
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

By design notifiers can be registerd once only,
2nd register attempt called by mistake silently corrupts notifiers list.

Proposed check cannot prevent described problem,
however it allows to detect its reason quickly without coredump analyze.

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
---
 kernel/notifier.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/notifier.c b/kernel/notifier.c
index 6196af8a8223..bfc95b3e4235 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -22,6 +22,7 @@ static int notifier_chain_register(struct notifier_block **nl,
 		struct notifier_block *n)
 {
 	while ((*nl) != NULL) {
+		WARN_ONCE(((*nl) == n), "double register detected");
 		if (n->priority > (*nl)->priority)
 			break;
 		nl = &((*nl)->next);
-- 
2.17.1