kernel/watchdog: always restore watchdog_softlockup(,hardlockup)_user_enabled after proc show

Otherwise when watchdog_enabled becomes 0,
watchdog_softlockup(,hardlockup)_user_enabled will changes to 0 after proc
show.

Steps to reproduce:

  step 1:
  # cat /proc/sys/kernel/*watchdog
  1
  1
  1

  | name                             | value
  |----------------------------------|--------------------------
  | watchdog_enabled                 | 1
  |----------------------------------|--------------------------
  | watchdog_hardlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_softlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_user_enabled            | 1
  |----------------------------------|--------------------------

  step 2:
  # echo 0 > /proc/sys/kernel/watchdog

  | name                             | value
  |----------------------------------|--------------------------
  | watchdog_enabled                 | 0
  |----------------------------------|--------------------------
  | watchdog_hardlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_softlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_user_enabled            | 0
  |----------------------------------|--------------------------

  step 3:
  # cat /proc/sys/kernel/*watchdog
  0
  0
  0

  | name                             | value
  |----------------------------------|--------------------------
  | watchdog_enabled                 | 0
  |----------------------------------|--------------------------
  | watchdog_hardlockup_user_enabled | 0
  |----------------------------------|--------------------------
  | watchdog_softlockup_user_enabled | 0
  |----------------------------------|--------------------------
  | watchdog_user_enabled            | 0
  |----------------------------------|--------------------------

  step 4:
  # echo 1 > /proc/sys/kernel/watchdog

  | name                             | value
  |----------------------------------|--------------------------
  | watchdog_enabled                 | 0
  |----------------------------------|--------------------------
  | watchdog_hardlockup_user_enabled | 0
  |----------------------------------|--------------------------
  | watchdog_softlockup_user_enabled | 0
  |----------------------------------|--------------------------
  | watchdog_user_enabled            | 0
  |----------------------------------|--------------------------

  step 5:
  # cat /proc/sys/kernel/*watchdog
  0
  0
  0

If we dont do "step 3", do "step 4" right after "step 2", it will be

  | name                             | value
  |----------------------------------|--------------------------
  | watchdog_enabled                 | 1
  |----------------------------------|--------------------------
  | watchdog_hardlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_softlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_user_enabled            | 1
  |----------------------------------|--------------------------

then everything works correctly.

So this patch fix "step 3"'s value into

| name                             | value
|----------------------------------|--------------------------
| watchdog_enabled                 | 0
|----------------------------------|--------------------------
| watchdog_hardlockup_user_enabled | 1
|----------------------------------|--------------------------
| watchdog_softlockup_user_enabled | 1
|----------------------------------|--------------------------
| watchdog_user_enabled            | 0
|----------------------------------|--------------------------

And still print 0 as before.

Link: https://lkml.kernel.org/r/20240906094700.GA30052@didi-ThinkCentre-M930t-N000
Signed-off-by: Tio Zhang <tiozhang@didiglobal.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Krister Johansen <kjlx@templeofstupid.com>
Cc: Li Zhe <lizhe.67@bytedance.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 262691ba62b7..6c91b6b72f51 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -990,6 +990,7 @@ static int proc_watchdog_common(int which, const struct ctl_table *table, int wr
 
 	mutex_lock(&watchdog_mutex);
 
+	old = *param;
 	if (!write) {
 		/*
 		 * On read synchronize the userspace interface. This is a
@@ -997,8 +998,8 @@ static int proc_watchdog_common(int which, const struct ctl_table *table, int wr
 		 */
 		*param = (watchdog_enabled & which) != 0;
 		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+		*param = old;
 	} else {
-		old = READ_ONCE(*param);
 		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 		if (!err && old != READ_ONCE(*param))
 			proc_watchdog_update();