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

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Date:	Fri, 18 Apr 2014 10:41:15 +0900
From:	Namjae Jeon <namjae.jeon@...sung.com>
To:	'Lukáš Czerner' <lczerner@...hat.com>,
	'Jan Kara' <jack@...e.cz>
Cc:	'Theodore Ts'o' <tytso@....edu>,
	'linux-ext4' <linux-ext4@...r.kernel.org>
Subject: RE: [PATCH 2/3] ext4: fix ZERO_RANGE test failure in data journalling
 mode



> -----Original Message-----
> From: Lukáš Czerner [mailto:lczerner@...hat.com]
> Sent: Thursday, April 17, 2014 9:16 PM
> To: Namjae Jeon
> Cc: 'Theodore Ts'o'; 'linux-ext4'
> 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 21:01:25 +0900
> > From: Namjae Jeon <namjae.jeon@...sung.com>
> > To: 'Lukáš Czerner' <lczerner@...hat.com>
> > Cc: 'Theodore Ts'o' <tytso@....edu>, 'linux-ext4' <linux-ext4@...r.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 19:52:09 +0900
> > > > From: Namjae Jeon <namjae.jeon@...sung.com>
> > > > To: 'Lukáš Czerner' <lczerner@...hat.com>
> > > > Cc: 'Theodore Ts'o' <tytso@....edu>, 'linux-ext4' <linux-ext4@...r.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@...sung.com>
> > > > > > To: Theodore Ts'o <tytso@....edu>
> > > > > > Cc: linux-ext4 <linux-ext4@...r.kernel.org>,
> > > > > >     Lukáš Czerner <lczerner@...hat.com>
> > > > > > Subject: [PATCH 2/3] ext4: fix ZERO_RANGE test failure in data journalling
> > > > > >     mode
> > > > > >
> > > > > > From: Namjae Jeon <namjae.jeon@...sung.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@...sung.com>
> > > > > > Signed-off-by: Ashish Sangwan <a.sangwan@...sung.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 ?
> > Yes, I can see ext4_force_commit inside mutex_lock in ext4_sync_file().
> 
> There might be some misunderstanding, are we talking about
> inode->i_mutex because that is certainly not held in
> ext4_sync_file() or am I missing something ?
Ah. Sorry, I checked old kernel source(v3.10)
i_mutex was removed from ext4_sync_file by Jan.
But that does not mean we can't call ext4_force_commit from within i_mutex.

Hi Jan.
Am I missing something ?

Thanks.

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

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