linux-kernel - Re: [PATCH] watchdog: when watchdog_enabled is 0, let (soft,nmi)switch remain 1 after we read them in proc

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Message-ID: <720FE0AC-FFB4-4236-9A29-9BE8C5D27C07@didiglobal.com>
Date: Wed, 4 Sep 2024 09:23:18 +0000
From: 张元瀚 Tio Zhang <tiozhang@...iglobal.com>
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Subject: Re: [PATCH] watchdog: when watchdog_enabled is 0, let
 (soft,nmi)switch remain 1 after we read them in proc

Hi, 

Ping :)

// get_maintainer.pl does not tell who are the maintainers or reviewers of kernel/watchdog.c
Add commit signers and sched maintainers to the CC list.

On 8/22/24 下午3:09, "张元瀚 Tio Zhang" <tiozhang@...iglobal.com <mailto:tiozhang@...iglobal.com>> wrote:


For users set "watchdog_user_enabled=0" but remaining
"(soft,nmi)watchdog_user_enabled=1". Watchdog threads(,nmi watchdog)
rework only if users reset "watchdog_user_enabled=1" without printing
those watchdog swicthes. Otherwise (soft,nmi)watchdog_user_enabled
will turn to 0 because of printing their values (It makes sense to print 0
since they do not work any more, but it does not make sense to let user's
swicthes change to 0 only by prints).


And after that, watchdog only should work again by doing:
(soft,nmi)watchdog_user_enabled=1
*** can't print, or everything go back to 0 again ***
watchdog_user_enabled=1


So this patch fixes this situation:


| name | value
|----------------------------|--------------------------
| watchdog_enabled | 0
|----------------------------|--------------------------
| nmi_watchdog_user_enabled | 1
|----------------------------|--------------------------
| soft_watchdog_user_enabled | 1
|----------------------------|--------------------------
| watchdog_user_enabled | 0
|----------------------------|--------------------------


cat /proc/sys/kernel/*watchdog
|
|
V
| name | value
|----------------------------|--------------------------
| watchdog_enabled | 0
|----------------------------|--------------------------
| nmi_watchdog_user_enabled | 0
|----------------------------|--------------------------
| soft_watchdog_user_enabled | 0
|----------------------------|--------------------------
| watchdog_user_enabled | 0
|----------------------------|--------------------------




Signed-off-by: Tio Zhang <tiozhang@...iglobal.com <mailto:tiozhang@...iglobal.com>>
---
kernel/watchdog.c | 10 ++++++++++
1 file changed, 10 insertions(+)


diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 51915b44ac73..42e69e83e76d 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -995,8 +995,18 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
* On read synchronize the userspace interface. This is a
* racy snapshot.
*/
+ old = READ_ONCE(*param);
*param = (watchdog_enabled & which) != 0;
err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+ /*
+ * When "old" is 1 and watchdog_enabled is 0,
+ * it should not be change to 0 for printing
+ * nmi_watchdog_user_enabled or soft_watchdog_user_enabled.
+ * So after we print it as 0,
+ * we should recover it to 1.
+ */
+ if (old && !watchdog_enabled)
+ *param = old;
} else {
old = READ_ONCE(*param);
err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
-- 
2.17.1