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From:   madhuparnabhowmik10@gmail.com
To:     wim@linux-watchdog.org, linux@roeck-us.net
Cc:     linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org,
        andrianov@ispras.ru, ldv-project@linuxtesting.org,
        Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Subject: [PATCH] drivers: watchdog: pc87413_wdt: Fix Race condition bug
Date:   Thu, 13 Aug 2020 18:24:51 +0530
Message-Id: <20200813125451.19118-1-madhuparnabhowmik10@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

After misc_register the open() callback can be called.
However the base address (swc_base_addr) is set after misc_register()
in init.
As a result, if open callback is called before pc87413_get_swc_base_addr()
then in the following call chain: pc87413_open() -> pc87413_refresh() ->
pc87413_swc_bank3() : The value of swc_base_addr will be -1.
Therefore, do misc_register() after pc87413_get_swc_base_addr().

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
---
 drivers/watchdog/pc87413_wdt.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/watchdog/pc87413_wdt.c b/drivers/watchdog/pc87413_wdt.c
index 73fbfc99083b..ad8b8af2bdc0 100644
--- a/drivers/watchdog/pc87413_wdt.c
+++ b/drivers/watchdog/pc87413_wdt.c
@@ -512,6 +512,10 @@ static int __init pc87413_init(void)
 	if (ret != 0)
 		pr_err("cannot register reboot notifier (err=%d)\n", ret);
 
+	pc87413_select_wdt_out();
+	pc87413_enable_swc();
+	pc87413_get_swc_base_addr();
+
 	ret = misc_register(&pc87413_miscdev);
 	if (ret != 0) {
 		pr_err("cannot register miscdev on minor=%d (err=%d)\n",
@@ -520,10 +524,6 @@ static int __init pc87413_init(void)
 	}
 	pr_info("initialized. timeout=%d min\n", timeout);
 
-	pc87413_select_wdt_out();
-	pc87413_enable_swc();
-	pc87413_get_swc_base_addr();
-
 	if (!request_region(swc_base_addr, 0x20, MODNAME)) {
 		pr_err("cannot request SWC region at 0x%x\n", swc_base_addr);
 		ret = -EBUSY;
-- 
2.17.1