[PATCH v2 1/1] kernel/watchdog: always restore watchdog_softlockup(,hardlockup)_user_enabled after proc show

[Tio Zhang]

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.

Signed-off-by: Tio Zhang <tiozhang@xxxxxxxxxxxxxx>
---
 kernel/watchdog.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 51915b44ac73..ade69b2319f6 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -990,6 +990,7 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 
 	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, struct ctl_table *table, int write,
 		 */
 		*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();
-- 
2.17.1