linux-kernel - Re: Faulty commit "watchdog: iTCO_wdt: Account for rebooting on second timeout"

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Date:   Tue, 3 Aug 2021 08:27:12 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Jan Kiszka <jan.kiszka@...mens.com>,
        Jean Delvare <jdelvare@...e.de>,
        linux-watchdog@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Michael Marley <michael@...haelmarley.com>
Subject: Re: Faulty commit "watchdog: iTCO_wdt: Account for rebooting on
 second timeout"

On 8/3/21 8:01 AM, Jan Kiszka wrote:
> On 03.08.21 16:59, Jan Kiszka wrote:
>> On 03.08.21 16:51, Jean Delvare wrote:
>>> Hi all,
>>>
>>> Commit cb011044e34c ("watchdog: iTCO_wdt: Account for rebooting on
>>> second timeout") causes a regression on several systems. Symptoms are:
>>> system reboots automatically after a short period of time if watchdog
>>> is enabled (by systemd for example). This has been reported in bugzilla:
>>>
>>> https://bugzilla.kernel.org/show_bug.cgi?id=213809
>>>
>>> Unfortunately this commit was backported to all stable kernel branches
>>> (4.14, 4.19, 5.4, 5.10, 5.12 and 5.13). I'm not sure why that is the
>>> case, BTW, as there is no Fixes tag and no Cc to stable@...r either.
>>> And the fix is not trivial, has apparently not seen enough testing,
>>> and addresses a problem that has a known and simple workaround. IMHO it
>>> should never have been accepted as a stable patch in the first place.
>>> Especially when the previous attempt to fix this issue already ended
>>> with a regression and a revert.
>>>
>>> Anyway... After a glance at the patch, I see what looks like a nice
>>> thinko:
>>>
>>> +	if (p->smi_res &&
>>> +	    (SMI_EN(p) & (TCO_EN | GBL_SMI_EN)) != (TCO_EN | GBL_SMI_EN))
>>>
>>> The author most certainly meant inl(SMI_EN(p)) (the register's value)
>>> and not SMI_EN(p) (the register's address).
>>>

Yes, shame on me that I didn't see that.

>>
>> https://lkml.org/lkml/2021/7/26/349
>>
> 
> That's for the fix (in line with your analysis).
> 
> I was also wondering if backporting that quickly was needed. Didn't
> propose it, though.
> 

I'd suggest to discuss that with Greg and Sasha. Backporting is pretty
aggressive nowadays.

Guenter