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Date: Thu, 20 Jun 2019 16:00:28 +0200 From: Jan Kara <jack@...e.cz> To: "Darrick J. Wong" <darrick.wong@...cle.com> Cc: matthew.garrett@...ula.com, yuchao0@...wei.com, tytso@....edu, ard.biesheuvel@...aro.org, josef@...icpanda.com, clm@...com, adilger.kernel@...ger.ca, viro@...iv.linux.org.uk, jack@...e.com, dsterba@...e.com, jaegeuk@...nel.org, jk@...abs.org, reiserfs-devel@...r.kernel.org, linux-efi@...r.kernel.org, devel@...ts.orangefs.org, linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org, linux-mm@...ck.org, linux-nilfs@...r.kernel.org, linux-mtd@...ts.infradead.org, ocfs2-devel@....oracle.com, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org Subject: Re: [PATCH 2/6] vfs: flush and wait for io when setting the immutable flag via SETFLAGS On Mon 10-06-19 21:46:25, Darrick J. Wong wrote: > From: Darrick J. Wong <darrick.wong@...cle.com> > > 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 <darrick.wong@...cle.com> ... > 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... Honza -- Jan Kara <jack@...e.com> SUSE Labs, CR
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