From: Jan Kiszka <[email protected]>
We must not pet a running watchdog when handle_boot_enabled is off
because this requests to only start doing that via userspace, not during
probing.
Signed-off-by: Jan Kiszka <[email protected]>
---
drivers/watchdog/watchdog_dev.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 3bab32485273..3c93d00bb284 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -1172,7 +1172,10 @@ int watchdog_set_last_hw_keepalive(struct watchdog_device *wdd,
wd_data->last_hw_keepalive = ktime_sub(now, ms_to_ktime(last_ping_ms));
- return __watchdog_ping(wdd);
+ if (handle_boot_enabled)
+ return __watchdog_ping(wdd);
+
+ return 0;
}
EXPORT_SYMBOL_GPL(watchdog_set_last_hw_keepalive);
--
2.31.1
On 7/30/21 12:39 PM, Jan Kiszka wrote:
> From: Jan Kiszka <[email protected]>
>
> We must not pet a running watchdog when handle_boot_enabled is off
> because this requests to only start doing that via userspace, not during
> probing.
>
The scope of the changed function is quite limited. See the
definition of watchdog_set_last_hw_keepalive(). On top of that,
__watchdog_ping() does a bit more than just ping the watchdog,
and it only pings the watchdog in limited circumstances. On top of that,
the scope of handle_boot_enabled is different: If enabled, it tells
the watchdog core to keep pinging a watchdog until userspace opens
the device. This is about continuous pings, not about an initial one.
Given that, I'd rather have the watchdog subsystem issue an additional
ping than risking a regression.
The only driver calling watchdog_set_last_hw_keepalive() is rti_wdt.c.
Does this patch solve a specific problem observed with that watchdog ?
Guenter
> Signed-off-by: Jan Kiszka <[email protected]>
> ---
> drivers/watchdog/watchdog_dev.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 3bab32485273..3c93d00bb284 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -1172,7 +1172,10 @@ int watchdog_set_last_hw_keepalive(struct watchdog_device *wdd,
>
> wd_data->last_hw_keepalive = ktime_sub(now, ms_to_ktime(last_ping_ms));
>
> - return __watchdog_ping(wdd);
> + if (handle_boot_enabled)
> + return __watchdog_ping(wdd);
> +
> + return 0;
> }
> EXPORT_SYMBOL_GPL(watchdog_set_last_hw_keepalive);
>
>
On 30.07.21 22:49, Guenter Roeck wrote:
> On 7/30/21 12:39 PM, Jan Kiszka wrote:
>> From: Jan Kiszka <[email protected]>
>>
>> We must not pet a running watchdog when handle_boot_enabled is off
>> because this requests to only start doing that via userspace, not during
>> probing.
>>
>
> The scope of the changed function is quite limited. See the
> definition of watchdog_set_last_hw_keepalive(). On top of that,
> __watchdog_ping() does a bit more than just ping the watchdog,
> and it only pings the watchdog in limited circumstances. On top of that,
> the scope of handle_boot_enabled is different: If enabled, it tells
> the watchdog core to keep pinging a watchdog until userspace opens
> the device. This is about continuous pings, not about an initial one.
> Given that, I'd rather have the watchdog subsystem issue an additional
> ping than risking a regression.
>
> The only driver calling watchdog_set_last_hw_keepalive() is rti_wdt.c.
> Does this patch solve a specific problem observed with that watchdog ?
Yes, it unbreaks support for handle_boot_enabled=no by not starting the
automatic pinging of the kernel until userspace opens the device.
Without this fix, the core will prematurely start kernel-side pinging,
and hanging userspace will never be detected.
Jan
--
Siemens AG, T RDA IOT
Corporate Competence Center Embedded Linux
On 7/30/21 2:37 PM, Jan Kiszka wrote:
> On 30.07.21 22:49, Guenter Roeck wrote:
>> On 7/30/21 12:39 PM, Jan Kiszka wrote:
>>> From: Jan Kiszka <[email protected]>
>>>
>>> We must not pet a running watchdog when handle_boot_enabled is off
>>> because this requests to only start doing that via userspace, not during
>>> probing.
>>>
>>
>> The scope of the changed function is quite limited. See the
>> definition of watchdog_set_last_hw_keepalive(). On top of that,
>> __watchdog_ping() does a bit more than just ping the watchdog,
>> and it only pings the watchdog in limited circumstances. On top of that,
>> the scope of handle_boot_enabled is different: If enabled, it tells
>> the watchdog core to keep pinging a watchdog until userspace opens
>> the device. This is about continuous pings, not about an initial one.
>> Given that, I'd rather have the watchdog subsystem issue an additional
>> ping than risking a regression.
>>
>> The only driver calling watchdog_set_last_hw_keepalive() is rti_wdt.c.
>> Does this patch solve a specific problem observed with that watchdog ?
>
> Yes, it unbreaks support for handle_boot_enabled=no by not starting the
> automatic pinging of the kernel until userspace opens the device.
> Without this fix, the core will prematurely start kernel-side pinging,
> and hanging userspace will never be detected.
>
Good point. You are correct.
I think it should also check for watchdog_hw_running(wdd), though.
The function should not really be called if the watchdog isn't
running, but it should still not ping the watchdog in that case.
Something like
if (watchdog_hw_running(wdd) && handle_boot_enabled)
return __watchdog_ping(wdd);
return 0;
Also, I think it would make sense to add your additional comment
to the patch description. The problem isn't only that the watchdog
is pinged once, the problem is that it starts _automatic_
pinging which it really should not do.
Thanks,
Guenter