linux-kernel - Re: [PATCH 0/5] watchdog: dw_wdt: allow only one probe + various fixes

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Message-ID: <558D5990.30102@roeck-us.net>
Date:	Fri, 26 Jun 2015 06:54:24 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Ian Abbott <abbotti@....co.uk>, linux-watchdog@...r.kernel.org
CC:	Wim Van Sebroeck <wim@...ana.be>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] watchdog: dw_wdt: allow only one probe + various
 fixes

On 06/26/2015 06:21 AM, Ian Abbott wrote:
> The dw_wdt watchdog driver supports a single DesignWare watchdog device
> using a statically allocated variable 'dw_wdt' to manage it, but there
> are some bits of hardware containing two such devices.  If the "probe"
> is called for more than one device, the 'dw_wdt' variable gets
> clobbered, generally resulting in a kernel crash.  Change it to reject
> additional probed devices.
>
> We probably don't expect the "remove" function to get called, but if it
> does, make sure the Linux timer used by device gets unqueued.
>
> The timer also gets unqueued if the watchdog device is closed by the
> user process unexpectedly.  However, this is not currently done
> asynchronously and the timer function normally requeues the timer.  If
> it manages to requeue the timer, the next call of the timer function
> will behave as though the close was expected and continue patting the
> dog every half a second when it should have stopped doing so.  Unqueue
> the timer synchronously to avoid that.
>
> NOTE: There is another potential problem that I haven't bothered to fix.
> If the "remove" function is called while the watchdog device is still
> open, any in-progress or future file operations are likely to screw
> things up.
>
> 1) watchdog: dw_wdt: prepare for more atomic bits
> 2) watchdog: dw_wdt: reject additional device probes
> 3) watchdog: dw_wdt: only unregister restart handler if registered
> 4) watchdog: dw_wdt: unqueue timer on device removal
> 5) watchdog: dw_wdt: unqueue timer synchronously on unexpected close
>
>   drivers/watchdog/dw_wdt.c | 46 +++++++++++++++++++++++++++++++++++-----------
>   1 file changed, 35 insertions(+), 11 deletions(-)

Hi Ian,

any chance you can convert the driver to use the watchdog APIs instead ?
This way it could support more than one watchdog, and the code would be
much simpler.

Thanks,
Guenter

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