From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Holt Subject: Re: [patch 1/4] mmu_notifier: Core code Date: Sat, 26 Jan 2008 06:01:50 -0600 Message-ID: <20080126120149.GS3058@sgi.com> References: <20080125055606.102986685@sgi.com> <20080125055801.212744875@sgi.com> <20080125183934.GO26420@sgi.com> <20080125185646.GQ3058@sgi.com> <20080125193554.GP26420@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Nick Piggin , Andrea Arcangeli , Peter Zijlstra , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Benjamin Herrenschmidt , steiner-sJ/iWh9BUns@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Avi Kivity , kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, daniel.blueman-xqY44rlHlBpWk0Htik3J/w@public.gmane.org, Robin Holt , Hugh Dickins To: Christoph Lameter Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org > void mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm) > { > - spin_lock(&mmu_notifier_list_lock); > - hlist_add_head(&mn->hlist, &mm->mmu_notifier.head); > - spin_unlock(&mmu_notifier_list_lock); > + down_write(&mm->mmap_sem); > + __mmu_notifier_register(mn, mm); > + up_write(&mm->mmap_sem); > } > EXPORT_SYMBOL_GPL(mmu_notifier_register); But what if the caller is already holding the mmap_sem? Why force the acquire into this function? Since we are dealing with a semaphore/mutex, it is reasonable that other structures are protected by this, more work will be done, and therefore put the weight of acquiring the sema in the control of the caller where they can decide if more needs to be completed. That was why I originally suggested creating a new rwsem_is_write_locked() function and basing a BUG_ON upon that. Thanks, Robin ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/