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

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Submitter Namjae Jeon
Date April 16, 2014, 10:29 p.m.
Message ID <002a01cf59c3$4eaf7490$ec0e5db0$@samsung.com>
Download mbox | patch
Permalink /patch/339720/
State Superseded
Headers show

Comments

Namjae Jeon - April 16, 2014, 10:29 p.m.
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(+)
Lukas Czerner - April 17, 2014, 8:53 a.m.
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,

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 ?

-Lukas

> +
>  	/*
>  	 * Write out all dirty pages to avoid race conditions
>  	 * Then release them.
>
Namjae Jeon - April 17, 2014, 10:52 a.m.
> 
> 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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Lukas Czerner - April 17, 2014, 11 a.m.
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.
> > >
> 
>
Namjae Jeon - April 17, 2014, 12:01 p.m.
> 
> 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 ?
Yes, I can see ext4_force_commit inside mutex_lock in ext4_sync_file().

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

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Lukas Czerner - April 17, 2014, 12:16 p.m.
On Thu, 17 Apr 2014, Namjae Jeon wrote:

> Date: Thu, 17 Apr 2014 21:01:25 +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 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 ?
> 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 ?

-Lukas

> 
> > 
> > -Lukas
> > 
> > >
> > > Thanks!
> > > >
> > > > -Lukas
> > > >
> > > > > +
> > > > >  	/*
> > > > >  	 * Write out all dirty pages to avoid race conditions
> > > > >  	 * Then release them.
> > > > >
> > >
> > >
> 
>
Namjae Jeon - April 18, 2014, 1:41 a.m.
> -----Original Message-----
> From: Lukáš Czerner [mailto:lczerner@redhat.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@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 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 ?
> > 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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Theodore Ts'o - April 18, 2014, 2:37 p.m.
So a couple of things.  First of all, ext4_force_commit() is a very
expensive call, so calling it twice is really not a good idea.

Secondly, in the ext4_collapse_range() you are calling
ext4_force_commit() before filemap_write_and_wait_range().

	/* 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;
	}

	/* Write out all dirty pages */
	ret = filemap_write_and_wait_range(inode->i_mapping, offset, -1);
	if (ret)
		return ret;

Shouldn't we reverse these two calls?

Finally, I'm wondering if we would be better off creating a new
explicit EXT4_I(inode)->i_write_mutex which is used to block new
writes from starting.  This could also be used to subsume the
ext4_aio_mutex.

						- Ted
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Lukas Czerner - April 18, 2014, 4:25 p.m.
On Fri, 18 Apr 2014, Theodore Ts'o wrote:

> Date: Fri, 18 Apr 2014 10:37:11 -0400
> From: Theodore Ts'o <tytso@mit.edu>
> To: Namjae Jeon <namjae.jeon@samsung.com>
> Cc: 'Lukáš Czerner' <lczerner@redhat.com>, 'Jan Kara' <jack@suse.cz>,
>     'linux-ext4' <linux-ext4@vger.kernel.org>
> Subject: Re: [PATCH 2/3] ext4: fix ZERO_RANGE test failure in data journalling
>      mode
> 
> So a couple of things.  First of all, ext4_force_commit() is a very
> expensive call, so calling it twice is really not a good idea.
> 
> Secondly, in the ext4_collapse_range() you are calling
> ext4_force_commit() before filemap_write_and_wait_range().
> 
> 	/* 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;
> 	}
> 
> 	/* Write out all dirty pages */
> 	ret = filemap_write_and_wait_range(inode->i_mapping, offset, -1);
> 	if (ret)
> 		return ret;
> 
> Shouldn't we reverse these two calls?
> 
> Finally, I'm wondering if we would be better off creating a new
> explicit EXT4_I(inode)->i_write_mutex which is used to block new
> writes from starting.  This could also be used to subsume the
> ext4_aio_mutex.

We can maybe use something similar xfs has with their XFS_IOLOCK

-Lukas

> 
> 						- Ted
Namjae Jeon - April 19, 2014, 2:40 a.m.
> So a couple of things.  First of all, ext4_force_commit() is a very
> expensive call, so calling it twice is really not a good idea.
Yes, Right.
> 
> Secondly, in the ext4_collapse_range() you are calling
> ext4_force_commit() before filemap_write_and_wait_range().
> 
> 	/* 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;
> 	}
> 
> 	/* Write out all dirty pages */
> 	ret = filemap_write_and_wait_range(inode->i_mapping, offset, -1);
> 	if (ret)
> 		return ret;
> 
> Shouldn't we reverse these two calls?
Yes, The original problem will occur again if we reverse these calls.
ext4_force_commit will mark the buffers as dirty during commit transcation.
So we should sync it using filemap_write_and_wait_range later.
> 
> Finally, I'm wondering if we would be better off creating a new
> explicit EXT4_I(inode)->i_write_mutex which is used to block new
> writes from starting.  This could also be used to subsume the
> ext4_aio_mutex.
Right. It is better method. I will check your point. :)

Thanks Ted!!
> 
> 						- Ted

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Patch

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;
+	}
+
 	/*
 	 * Write out all dirty pages to avoid race conditions
 	 * Then release them.