RE: [PATCH 2/3] ext4: fix ZERO_RANGE test failure in data journalling mode

[Namjae Jeon <namjae.jeon@samsung.com>]

> 
> On Thu, 17 Apr 2014, Namjae Jeon wrote:
> 
> > Date: Thu, 17 Apr 2014 07:29:18 +0900
> > From: Namjae Jeon <namjae.jeon@samsung.com>
> > To: Theodore Ts'o <tytso@mit.edu>
> > Cc: linux-ext4 <linux-ext4@vger.kernel.org>,
> >     Lukáš Czerner <lczerner@redhat.com>
> > Subject: [PATCH 2/3] ext4: fix ZERO_RANGE test failure in data journalling
> >     mode
> >
> > From: Namjae Jeon <namjae.jeon@samsung.com>
> >
> > xfstests generic/091 is failing when mounting ext4 with data=journal.
> > I think that this regression is same problem that occurred prior to collapse
> > range issue. So ZERO RANGE also need to call ext4_force_commit as
> > collapse range.
> >
> > Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> > Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
> > ---
> >  fs/ext4/extents.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index f386dd6..a64242f 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -4742,6 +4742,13 @@ static long ext4_zero_range(struct file *file, loff_t offset,
> >
> >  	trace_ext4_zero_range(inode, offset, len, mode);
> >
> > +	/* Call ext4_force_commit to flush all data in case of data=journal. */
> > +	if (ext4_should_journal_data(inode)) {
> > +		ret = ext4_force_commit(inode->i_sb);
> > +		if (ret)
> > +			return ret;
> > +	}
> 
> Hi,
Hi Lukas.
> 
> it makes sense. But I have a question, maybe I do not understand it
> correctly but what protect us from other writes coming in after we
> force the commit ?
Yes, Currently new write can come between ext4_force_commit and till
we acquire mutex_lock. But this window is already present even
without patch. Its just that in case of data=journal mode, this
window will become slightly bigger. one possible solution coming to
my mind is one more time calling ext4_force_commit followed by a call
to filemap_write_and_wait_range inside mutex_lock which would sync
data that has dirtied after 1st call.

Thanks!
> 
> -Lukas
> 
> > +
> >  	/*
> >  	 * Write out all dirty pages to avoid race conditions
> >  	 * Then release them.
> >

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