From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: [PATCH 3/3] nfs: use ->mmap_prepare() to avoid an AB-BA deadlock Date: Wed, 14 Nov 2007 21:01:39 +0100 Message-ID: <20071114201528.514434000@chello.nl> References: <20071114200136.009242000@chello.nl> Cc: Linus Torvalds , Andrew Morton , Trond Myklebust , Nick Piggin , Hugh Dickins , Peter Zijlstra To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org Return-path: Received: from mx1.redhat.com ([66.187.233.31]:33410 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753258AbXKNUQv (ORCPT ); Wed, 14 Nov 2007 15:16:51 -0500 Content-Disposition: inline; filename=mmap_prepare_nfs.patch Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Normal locking order is: i_mutex mmap_sem However NFS's ->mmap hook, which is called under mmap_sem, can take i_mutex. Avoid this potential deadlock by doing the work that requires i_mutex from the new ->mmap_prepare(). [ Is this sufficient, or does it introduce a race? ] Signed-off-by: Peter Zijlstra --- fs/nfs/file.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) Index: linux-2.6/fs/nfs/file.c =================================================================== --- linux-2.6.orig/fs/nfs/file.c +++ linux-2.6/fs/nfs/file.c @@ -41,6 +41,9 @@ static int nfs_file_open(struct inode *, struct file *); static int nfs_file_release(struct inode *, struct file *); static loff_t nfs_file_llseek(struct file *file, loff_t offset, int origin); +static int +nfs_file_mmap_prepare(struct file * file, unsigned long len, + unsigned long prot, unsigned long flags, unsigned long pgoff); static int nfs_file_mmap(struct file *, struct vm_area_struct *); static ssize_t nfs_file_splice_read(struct file *filp, loff_t *ppos, struct pipe_inode_info *pipe, @@ -64,6 +67,7 @@ const struct file_operations nfs_file_op .write = do_sync_write, .aio_read = nfs_file_read, .aio_write = nfs_file_write, + .mmap_prepare = nfs_file_mmap_prepare, .mmap = nfs_file_mmap, .open = nfs_file_open, .flush = nfs_file_flush, @@ -270,7 +274,8 @@ nfs_file_splice_read(struct file *filp, } static int -nfs_file_mmap(struct file * file, struct vm_area_struct * vma) +nfs_file_mmap_prepare(struct file * file, unsigned long len, + unsigned long prot, unsigned long flags, unsigned long pgoff) { struct dentry *dentry = file->f_path.dentry; struct inode *inode = dentry->d_inode; @@ -279,13 +284,17 @@ nfs_file_mmap(struct file * file, struct dfprintk(VFS, "nfs: mmap(%s/%s)\n", dentry->d_parent->d_name.name, dentry->d_name.name); - status = nfs_revalidate_mapping(inode, file->f_mapping); - if (!status) { - vma->vm_ops = &nfs_file_vm_ops; - vma->vm_flags |= VM_CAN_NONLINEAR; - file_accessed(file); - } - return status; + return nfs_revalidate_mapping(inode, file->f_mapping); +} + +static int +nfs_file_mmap(struct file *file, struct vm_area_struct *vma) +{ + vma->vm_ops = &nfs_file_vm_ops; + vma->vm_flags |= VM_CAN_NONLINEAR; + file_accessed(file); + + return 0; } /* --