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Subject: Re: Faulty commit "watchdog: iTCO_wdt: Account for rebooting on
 second timeout"
To:     Jean Delvare <jdelvare@suse.de>, linux-watchdog@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>, stable@vger.kernel.org
Cc:     Guenter Roeck <linux@roeck-us.net>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        Michael Marley <michael@michaelmarley.com>
References: <20210803165108.4154cd52@endymion>
From:   Jan Kiszka <jan.kiszka@siemens.com>
Message-ID: <e13f45c4-70e2-e2c2-9513-ce38c8235b4f@siemens.com>
Date:   Tue, 3 Aug 2021 16:59:02 +0200
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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@vger 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).
> 

https://lkml.org/lkml/2021/7/26/349

Jan

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