From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keith Owens Date: Wed, 30 Jul 2008 16:12:21 +0000 Subject: Re: [patch] IA64: only call up() in salinfo_work_to_do() if down_trylock() was successful Message-Id: <20945.1217434341@ocs10w> List-Id: In-Reply-To: Your message of "Wed, 30 Jul 2008 02:43:29 MST." <20080730024329.404eccc3.akpm@linux-foundation.org> References: <20080729094718.GA5247@verge.net.au> In-Reply-To: <20080729094718.GA5247@verge.net.au> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Andrew Morton Cc: Simon Horman , linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, Tony Luck Andrew Morton (on Wed, 30 Jul 2008 02:43:29 -0700) wrote: >On Tue, 29 Jul 2008 23:07:45 +1000 Simon Horman 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 >> > > >> > >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. */