From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sat, 26 Jan 2008 06:01:50 -0600 From: Robin Holt Subject: Re: [patch 1/4] mmu_notifier: Core code 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-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: Robin Holt , Andrea Arcangeli , Avi Kivity , Izik Eidus , Nick Piggin , kvm-devel@lists.sourceforge.net, Benjamin Herrenschmidt , Peter Zijlstra , steiner@sgi.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, daniel.blueman@quadrics.com, Hugh Dickins List-ID: > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org