From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [Patch RFC 14/37] scsi: aacraid semaphore cleanup Date: Mon, 27 Jul 2009 00:21:06 +0200 (CEST) Message-ID: References: <20090726081459.455111897@linutronix.de> <20090726081555.073502498@linutronix.de> <1248639091.4766.4.camel@mulgrave.site> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Return-path: Received: from www.tglx.de ([62.245.132.106]:38950 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753976AbZGZW01 (ORCPT ); Sun, 26 Jul 2009 18:26:27 -0400 In-Reply-To: <1248639091.4766.4.camel@mulgrave.site> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: LKML , Andrew Morton , Ingo Molnar , Peter Zijlstra , linux-scsi On Sun, 26 Jul 2009, James Bottomley wrote: > cc linux-scsi added > > On Sun, 2009-07-26 at 08:18 +0000, Thomas Gleixner wrote: > > plain text document attachment > > (driver-scsi-aacraid-sema-cleanup.patch) > > The usage of these "mutex"es is non obvious and probably completions > > in some places. Make it them semaphores. > > -ENOCONTEXT on this ... I assume this is just a global > s/init_MUTEX/semaphore_init/? Well, in cases where the mutex use case is obvious it's a semaphore to mutex conversion. But this one is definitly not. > I think both are really just mutexes; no need for a counting semaphore. > There's no stack declaration issues (the fibs are long lived entities) > that would necessitate a completion. It's not about stack declaration. These semaphores can not be converted to mutexes for following reasons: 1) there is no mutex_init_locked() and there never will be one 2) the sem is taken from context A and released from context B. That violates the mutex semantics where the lock/unlock has to happen in the same thread context. i.e. wait_sem is taken from aac_do_ioctl() next_getadapter_fib() but release from aac_check_health() or aac_command_thread() I have no idea how that hell of code works, but wait_sem is definitely not a mutex and neither is event_wait. The beasts might serialize stuff as well, but they are also (ab)used as a completion to wait for whatever. Thanks, tglx