From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx195.postini.com [74.125.245.195]) by kanga.kvack.org (Postfix) with SMTP id 9A0CF6B002C for ; Thu, 8 Mar 2012 16:40:52 -0500 (EST) Date: Thu, 8 Mar 2012 13:40:50 -0800 From: Andrew Morton Subject: Re: [PATCH] hugetlbfs: lockdep annotate root inode properly Message-Id: <20120308134050.f53a0b2f.akpm@linux-foundation.org> In-Reply-To: <20120308211926.GB6546@boyd> References: <1331198116-13670-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20120308130256.c7855cbd.akpm@linux-foundation.org> <20120308211926.GB6546@boyd> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Tyler Hicks Cc: "Aneesh Kumar K.V" , linux-mm@kvack.org, davej@redhat.com, jboyer@redhat.com, linux-kernel@vger.kernel.org, Al Viro , Peter Zijlstra , Mimi Zohar , David Gibson On Thu, 8 Mar 2012 15:19:27 -0600 Tyler Hicks wrote: > > > > > > Sigh. Was lockdep_annotate_inode_mutex_key() sufficiently > > self-explanatory to justify leaving it undocumented? > > > > > > > > OK, the patch looks correct given the explanation in e096d0c7e2e, but > > I'd like to understand why it becomes necessary only now. > > > > > NOTE: This patch also require > > > http://thread.gmane.org/gmane.linux.file-systems/58795/focus=59565 > > > to remove the lockdep warning > > > > And that patch has been basically ignored. > > Al commented on it here: > > https://lkml.org/lkml/2012/2/16/518 > > He said that while my patch is correct, taking i_mutex inside mmap_sem > is still wrong. OK, thanks, yup. Taking i_mutex in file_operations.mmap() is wrong. Is hugetlbfs actually deadlockable because of this, or is it the case that the i_mutex->mmap_sem ordering happens to never happen for this filesystem? Although we shouldn't go and create incompatible lock ranking rules for different filesystems! So we need to pull the i_mutex out of hugetlbfs_file_mmap(). What's it actually trying to do in there? If we switch to i_size_read()/i_size_write() then AFAICT the problem comes down to hugetlb_reserve_pages(). hugetlb_reserve_pages() fiddles with i_mapping->private_list and the fs owns private_list and is free to use a lock other than i_mutex to protect it. (In fact i_mapping.private_lock is the usual lock for private_list). So from a quick scan here I'm thinking that a decent fix is to remove the i_mutex locking from hugetlbfs_file_mmap(), switch hugetlbfs_file_mmap() to i_size_read/write then use a hugetlb-private lock to protect i_mapping->private_list. region_chg() will do GFP_KERNEL allocations under that lock, so some care is needed. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org