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

["Lukáš Czerner" <lczerner@redhat.com>]

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On Thu, 17 Apr 2014, Namjae Jeon wrote:

> Date: Thu, 17 Apr 2014 19:52:09 +0900
> From: Namjae Jeon <namjae.jeon@samsung.com>
> To: 'Lukáš Czerner' <lczerner@redhat.com>
> Cc: 'Theodore Ts'o' <tytso@mit.edu>, 'linux-ext4' <linux-ext4@vger.kernel.org>
> Subject: RE: [PATCH 2/3] ext4: fix ZERO_RANGE test failure in data journalling
>      mode
> 
> > 
> > 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.

Can we really call ext4_force_commit() inside mutex_lock ?

-Lukas

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