From: Keith Owens <kaos@ocs.com.au>
To: Simon Horman <horms@verge.net.au>
cc: linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org,
       Tony Luck <tony.luck@intel.com>
Subject: Re: [patch] IA64: only call up() in salinfo_work_to_do() if down_trylock() was successful 
In-reply-to: Your message of "Tue, 29 Jul 2008 19:47:20 +1000."
             <20080729094718.GA5247@verge.net.au> 
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Date: Tue, 29 Jul 2008 22:47:09 +1000
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Simon Horman (on Tue, 29 Jul 2008 19:47:20 +1000) wrote:
>Aesthetic issues aside is it safe to call up() if down_trylock() failed?
>
>arch/ia64/kernel/salinfo.c: In function `salinfo_work_to_do':
>arch/ia64/kernel/salinfo.c:195: warning: ignoring return value of `down_trylock'
>
>Signed-off-by: Simon Horman <horms@verge.net.au>
>
>Index: linux-2.6/arch/ia64/kernel/salinfo.c
>===================================================================
>--- linux-2.6.orig/arch/ia64/kernel/salinfo.c	2008-07-29 19:06:33.000000000 +1000
>+++ linux-2.6/arch/ia64/kernel/salinfo.c	2008-07-29 19:40:02.000000000 +1000
>@@ -192,8 +192,8 @@ struct salinfo_platform_oemdata_parms {
> static void
> salinfo_work_to_do(struct salinfo_data *data)
> {
>-	down_trylock(&data->mutex);
>-	up(&data->mutex);
>+	if (down_trylock(&data->mutex) == 0)
>+		up(&data->mutex);
> }
> 
> static void

NAK.  The whole point of this function is to set the mutex to the up
state, irrespective of whether it was already down or not.  Tracking
the state of data->mutex in all the possible contexts is just too
fragile, especially since it can be modified from NMI context.
salinfo_work_to_do() ensures that the mtuex ends in the up state.

To remove the warning, just stick '(void)' in front of down_trylock().

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