From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Jan Kara <jack@suse.cz>
Cc: linux-efi@vger.kernel.org, linux-btrfs@vger.kernel.org,
yuchao0@huawei.com, linux-mm@kvack.org, clm@fb.com,
adilger.kernel@dilger.ca, matthew.garrett@nebula.com,
linux-nilfs@vger.kernel.org, linux-ext4@vger.kernel.org,
devel@lists.orangefs.org, josef@toxicpanda.com,
reiserfs-devel@vger.kernel.org, viro@zeniv.linux.org.uk,
dsterba@suse.com, jaegeuk@kernel.org, tytso@mit.edu,
ard.biesheuvel@linaro.org, linux-kernel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net,
linux-xfs@vger.kernel.org, jk@ozlabs.org, jack@suse.com,
linux-fsdevel@vger.kernel.org, linux-mtd@lists.infradead.org,
ocfs2-devel@oss.oracle.com
Subject: Re: [Ocfs2-devel] [PATCH 2/7] vfs: flush and wait for io when setting the immutable flag via SETFLAGS
Date: Mon, 24 Jun 2019 20:04:39 -0700 [thread overview]
Message-ID: <20190625030439.GA5379@magnolia> (raw)
In-Reply-To: <20190624215817.GE1611011@magnolia>
On Mon, Jun 24, 2019 at 02:58:17PM -0700, Darrick J. Wong wrote:
> On Mon, Jun 24, 2019 at 01:37:37PM +0200, Jan Kara wrote:
> > On Fri 21-06-19 16:57:07, Darrick J. Wong wrote:
> > > From: Darrick J. Wong <darrick.wong@oracle.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@oracle.com>
> >
> > Seeing the way this worked out, is there a reason to have separate
> > vfs_ioc_setflags_flush_data() instead of folding the functionality in
> > vfs_ioc_setflags_check() (possibly renaming it to
> > vfs_ioc_setflags_prepare() to indicate it does already some changes)? I
> > don't see any place that would need these two separated...
>
> XFS needs them to be separated.
>
> If we even /think/ that we're going to be setting the immutable flag
> then we need to grab the IOLOCK and the MMAPLOCK to prevent further
> writes while we drain all the directio writes and dirty data. IO
> completions for the write draining can take the ILOCK, which means that
> we can't have grabbed it yet.
>
> Next, we grab the ILOCK so we can check the new flags against the inode
> and then update the inode core.
>
> For most filesystems I think it suffices to inode_lock and then do both,
> though.
Heh, lol, that applies to fssetxattr, not to setflags, because xfs
setflags implementation open-codes the relevant fssetxattr pieces.
So for setflags we can combine both parts into a single _prepare
function.
--D
> > > +/*
> > > + * Flush all pending IO and dirty mappings before setting S_IMMUTABLE on an
> > > + * inode via FS_IOC_SETFLAGS. If the flush fails we'll clear the flag before
> > > + * returning error.
> > > + *
> > > + * Note: the caller should be holding i_mutex, or else be sure that
> > > + * they have exclusive access to the inode structure.
> > > + */
> > > +static inline int vfs_ioc_setflags_flush_data(struct inode *inode, int flags)
> > > +{
> > > + int ret;
> > > +
> > > + if (!vfs_ioc_setflags_need_flush(inode, flags))
> > > + return 0;
> > > +
> > > + inode_set_flags(inode, S_IMMUTABLE, S_IMMUTABLE);
> > > + ret = inode_flush_data(inode);
> > > + if (ret)
> > > + inode_set_flags(inode, 0, S_IMMUTABLE);
> > > + return ret;
> > > +}
> >
> > Also this sets S_IMMUTABLE whenever vfs_ioc_setflags_need_flush() returns
> > true. That is currently the right thing but seems like a landmine waiting
> > to trip? So I'd just drop the vfs_ioc_setflags_need_flush() abstraction to
> > make it clear what's going on.
>
> Ok.
>
> --D
>
> >
> > Honza
> > --
> > Jan Kara <jack@suse.com>
> > SUSE Labs, CR
>
> _______________________________________________
> Ocfs2-devel mailing list
> Ocfs2-devel@oss.oracle.com
> https://oss.oracle.com/mailman/listinfo/ocfs2-devel
next prev parent reply other threads:[~2019-06-25 3:06 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-21 23:56 [PATCH v4 0/7] vfs: make immutable files actually immutable Darrick J. Wong
2019-06-21 23:56 ` [PATCH 1/7] mm/fs: don't allow writes to immutable files Darrick J. Wong
2019-06-24 11:13 ` Jan Kara
2019-06-21 23:57 ` [PATCH 2/7] vfs: flush and wait for io when setting the immutable flag via SETFLAGS Darrick J. Wong
2019-06-24 11:37 ` Jan Kara
2019-06-24 21:58 ` Darrick J. Wong
2019-06-25 3:04 ` Darrick J. Wong [this message]
2019-06-25 7:08 ` [Ocfs2-devel] " Jan Kara
2019-06-24 15:33 ` Jan Kara
2019-06-24 16:36 ` Darrick J. Wong
2019-06-21 23:57 ` [PATCH 3/7] vfs: flush and wait for io when setting the immutable flag via FSSETXATTR Darrick J. Wong
2019-06-21 23:57 ` [PATCH 4/7] vfs: don't allow most setxattr to immutable files Darrick J. Wong
2019-06-21 23:57 ` [PATCH 5/7] xfs: refactor setflags to use setattr code directly Darrick J. Wong
2019-06-21 23:57 ` [PATCH 6/7] xfs: clean up xfs_merge_ioc_xflags Darrick J. Wong
2019-06-21 23:57 ` [PATCH 7/7] vfs: don't allow writes to swap files Darrick J. Wong
2019-06-25 10:36 ` [PATCH v4 0/7] vfs: make immutable files actually immutable Christoph Hellwig
2019-06-25 18:03 ` Darrick J. Wong
2019-06-25 20:37 ` Andreas Dilger
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