Andrew Morton (on Wed, 30 Jul 2008 02:43:29 -0700) wrote:
>On Tue, 29 Jul 2008 23:07:45 +1000 Simon Horman <horms@xxxxxxxxxxxx> wrote:
>
>> On Tue, Jul 29, 2008 at 10:47:09PM +1000, Keith Owens wrote:
>> > 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@xxxxxxxxxxxx>
>> > >
>> > >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.
>
>boggle. I daren't look.
>
>> > To remove the warning, just stick '(void)' in front of down_trylock().
>>
>> Thanks, will do.
>>
>
>For gawd's sake add a comment there too.
You mean like the comment that is already in there?
/* Kick the mutex that tells user space that there is work to do. Instead of
* trying to track the state of the mutex across multiple cpus, in user
* context, interrupt context, non-maskable interrupt context and hotplug cpu,
* it is far easier just to grab the mutex if it is free then release it.
*
* This routine must be called with data_saved_lock held, to make the down/up
* operation atomic.
*/
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