linux-kernel - Re: [PATCH] watchdog: only print critical log when the watchdog fails to be stopped

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Message-ID: <13073a1dfb7946af98565921c609bd6f@huawei.com>
Date: Wed, 5 Feb 2025 02:02:50 +0000
From: "liuchao (CR)" <liuchao173@...wei.com>
To: "linux@...ck-us.net" <linux@...ck-us.net>
CC: caihe <caihe@...wei.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-watchdog@...r.kernel.org"
	<linux-watchdog@...r.kernel.org>, lixiaokeng <lixiaokeng@...wei.com>,
	"wim@...ux-watchdog.org" <wim@...ux-watchdog.org>
Subject: Re: [PATCH] watchdog: only print critical log when the watchdog fails
 to be stopped

On 1/27/2025 22:30, Guenter Roeck wrote:
> On 1/27/25 01:35, liuchao (CR) wrote:
> > On 1/26/25 21:10, Guenter Roeck wrote:
> >> On 1/26/25 00:38, Liu Chao wrote:
> >>> Every time the user echoes 0 > /dev/watchdog0, meaningless critical
> >>> log is printed.
> >>>
> >>
> >> It is not meaningless, and it will still be displayed after this
> >> change, making the change pointless.
> >
> > The change is not pointless. For example, the softdog driver does not
> > invoke watchdog_stop or print logs in the watchdog_release.
> >
> 
> It seems to me that is a problem in the softdog driver.
> 
> The change is actually worse than I initially thought.
> The message is _supposed_ to be displayed if watchdog_stop() is not called while
> the watchdog is running (i.e., if err == -EBUSY).
> Otherwise it would not be displayed for real hardware watchdogs which are not
> stopped because they were running and watchdog_stop() is not called because
> WDIOF_MAGICCLOSE is set in the driver and the magic release byte was not
> written.
> 
> Specifically, the softdog driver has WDIOF_MAGICCLOSE set. It is not supposed
> to be unloadable (or unloaded) while the watchdog is running.

When echo to /dev/watchdog0, The watchdog_open, watchdog_write, and
watchdog_release functions are invoked in sequence. Do you mean the softdog
driver should not call watchdog_release?

After the user opens /dev/watchdog0, the user feeds the watchdog through ioctl
WDIOC_KEEPALIVE and never closes. Is this the correct usage?

> 
> Guenter