linux-kernel - Re: [PATCH v2 1/2] watchdog: dw

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Message-ID: <554C40B7.9060806@roeck-us.net>
Date:	Thu, 07 May 2015 21:51:03 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Doug Anderson <dianders@...omium.org>, wim@...ana.be
CC:	jszhang@...vell.com, Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] watchdog: dw_wdt: No need for a spinlock

On 05/07/2015 09:27 PM, Doug Anderson wrote:
> Right now the dw_wdt uses a spinlock to protect dw_wdt_open().  The
> problem is that while holding the spinlock we call:
> -> dw_wdt_set_top()
>     -> dw_wdt_top_in_seconds()
>        -> clk_get_rate()
>           -> clk_prepare_lock()
>              -> mutex_lock()
>
> Locking a mutex while holding a spinlock is not allowed and leads to
> warnings like "BUG: spinlock wrong CPU on CPU#1", among other
> problems.
>
> There's no reason to use a spinlock.  Only dw_wdt_open() was protected
> and the test_and_set_bit() at the start of that function protects us
> anyway.
>
> Signed-off-by: Doug Anderson <dianders@...omium.org>

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

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