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

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Date:   Fri, 6 Aug 2021 08:28:39 +0200
From:   Greg KH <greg@...ah.com>
To:     Jean Delvare <jdelvare@...e.de>
Cc:     linux-watchdog@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Guenter Roeck <linux@...ck-us.net>,
        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 Tue, Aug 03, 2021 at 04:51:08PM +0200, 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).

Let me go revert this from the stable trees now, thanks for the report.

greg k-h