From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2120.oracle.com ([156.151.31.85]:38802 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725906AbfFTWLL (ORCPT ); Thu, 20 Jun 2019 18:11:11 -0400 Date: Thu, 20 Jun 2019 15:09:40 -0700 From: "Darrick J. Wong" Subject: Re: [PATCH 2/6] vfs: flush and wait for io when setting the immutable flag via SETFLAGS Message-ID: <20190620220940.GC5375@magnolia> References: <156022836912.3227213.13598042497272336695.stgit@magnolia> <156022838496.3227213.3771632042609589318.stgit@magnolia> <20190620140028.GH30243@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190620140028.GH30243@quack2.suse.cz> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Jan Kara Cc: matthew.garrett@nebula.com, yuchao0@huawei.com, tytso@mit.edu, ard.biesheuvel@linaro.org, josef@toxicpanda.com, clm@fb.com, adilger.kernel@dilger.ca, viro@zeniv.linux.org.uk, jack@suse.com, dsterba@suse.com, jaegeuk@kernel.org, jk@ozlabs.org, reiserfs-devel@vger.kernel.org, linux-efi@vger.kernel.org, devel@lists.orangefs.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-nilfs@vger.kernel.org, linux-mtd@lists.infradead.org, ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org On Thu, Jun 20, 2019 at 04:00:28PM +0200, Jan Kara wrote: > On Mon 10-06-19 21:46:25, Darrick J. Wong wrote: > > From: Darrick J. Wong > > > > When we're using FS_IOC_SETFLAGS to set the immutable flag on a file, we > > need to ensure that userspace can't continue to write the file after the > > file becomes immutable. To make that happen, we have to flush all the > > dirty pagecache pages to disk to ensure that we can fail a page fault on > > a mmap'd region, wait for pending directio to complete, and hope the > > caller locked out any new writes by holding the inode lock. > > > > Signed-off-by: Darrick J. Wong > > ... > > > diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c > > index 6aa1df1918f7..a05341b94d98 100644 > > --- a/fs/ext4/ioctl.c > > +++ b/fs/ext4/ioctl.c > > @@ -290,6 +290,9 @@ static int ext4_ioctl_setflags(struct inode *inode, > > jflag = flags & EXT4_JOURNAL_DATA_FL; > > > > err = vfs_ioc_setflags_check(inode, oldflags, flags); > > + if (err) > > + goto flags_out; > > + err = vfs_ioc_setflags_flush_data(inode, flags); > > if (err) > > goto flags_out; > > > > ... > > > diff --git a/include/linux/fs.h b/include/linux/fs.h > > index 8dad3c80b611..9c899c63957e 100644 > > --- a/include/linux/fs.h > > +++ b/include/linux/fs.h > > @@ -3548,7 +3548,41 @@ static inline struct sock *io_uring_get_socket(struct file *file) > > > > int vfs_ioc_setflags_check(struct inode *inode, int oldflags, int flags); > > > > +/* > > + * Do we need to flush the file data before changing attributes? When we're > > + * setting the immutable flag we must stop all directio writes and flush the > > + * dirty pages so that we can fail the page fault on the next write attempt. > > + */ > > +static inline bool vfs_ioc_setflags_need_flush(struct inode *inode, int flags) > > +{ > > + if (S_ISREG(inode->i_mode) && !IS_IMMUTABLE(inode) && > > + (flags & FS_IMMUTABLE_FL)) > > + return true; > > + > > + return false; > > +} > > + > > +/* > > + * Flush file data before changing attributes. Caller must hold any locks > > + * required to prevent further writes to this file until we're done setting > > + * flags. > > + */ > > +static inline int inode_flush_data(struct inode *inode) > > +{ > > + inode_dio_wait(inode); > > + return filemap_write_and_wait(inode->i_mapping); > > +} > > + > > +/* Flush file data before changing attributes, if necessary. */ > > +static inline int vfs_ioc_setflags_flush_data(struct inode *inode, int flags) > > +{ > > + if (vfs_ioc_setflags_need_flush(inode, flags)) > > + return inode_flush_data(inode); > > + return 0; > > +} > > + > > But this is racy at least for page faults, isn't it? What protects you > against write faults just after filemap_write_and_wait() has finished? > So either you need to set FS_IMMUTABLE_FL before flushing data or you need > to get more protection from the fs than just i_rwsem. In the case of ext4 > that would be i_mmap_rwsem but other filesystems don't have equivalent > protection... Yes, I see that now. I think it'll work to set S_IMMUTABLE before trying the flush, so long as I am careful to put the call sites right before we update the inode flags. --D > > Honza > -- > Jan Kara > SUSE Labs, CR