linux-kernel - [PATCH 3/5] watchdog: implement error handling in update_watchdog_all

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Message-Id: <1443473052-3053-4-git-send-email-uobergfe@redhat.com>
Date:	Mon, 28 Sep 2015 22:44:10 +0200
From:	Ulrich Obergfell <uobergfe@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, dzickus@...hat.com, atomlin@...hat.com,
	uobergfe@...hat.com
Subject: [PATCH 3/5] watchdog: implement error handling in update_watchdog_all_cpus() and callers

update_watchdog_all_cpus() now passes errors from watchdog_park_threads()
up to functions in the call chain. This allows watchdog_enable_all_cpus()
and proc_watchdog_update() to handle such errors too.

Signed-off-by: Ulrich Obergfell <uobergfe@...hat.com>
---
 kernel/watchdog.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index eb9527c..457113c 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -731,10 +731,17 @@ void lockup_detector_resume(void)
 	mutex_unlock(&watchdog_proc_mutex);
 }
 
-static void update_watchdog_all_cpus(void)
+static int update_watchdog_all_cpus(void)
 {
-	watchdog_park_threads();
+	int ret;
+
+	ret = watchdog_park_threads();
+	if (ret)
+		return ret;
+
 	watchdog_unpark_threads();
+
+	return 0;
 }
 
 static int watchdog_enable_all_cpus(void)
@@ -753,9 +760,17 @@ static int watchdog_enable_all_cpus(void)
 		 * Enable/disable the lockup detectors or
 		 * change the sample period 'on the fly'.
 		 */
-		update_watchdog_all_cpus();
+		err = update_watchdog_all_cpus();
+
+		if (err) {
+			watchdog_disable_all_cpus();
+			pr_err("Failed to update lockup detectors, disabled\n");
+		}
 	}
 
+	if (err)
+		watchdog_enabled = 0;
+
 	return err;
 }
 
@@ -851,12 +866,13 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 		} while (cmpxchg(&watchdog_enabled, old, new) != old);
 
 		/*
-		 * Update the run state of the lockup detectors.
-		 * Restore 'watchdog_enabled' on failure.
+		 * Update the run state of the lockup detectors. There is _no_
+		 * need to check the value returned by proc_watchdog_update()
+		 * and to restore the previous value of 'watchdog_enabled' as
+		 * both lockup detectors are disabled if proc_watchdog_update()
+		 * returns an error.
 		 */
 		err = proc_watchdog_update();
-		if (err)
-			watchdog_enabled = old;
 	}
 out:
 	mutex_unlock(&watchdog_proc_mutex);
-- 
1.7.11.7

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