Re: [PATCH 07/15] ext4: Take i_mutex before punching hole

[Zheng Liu <gnehzuil.liu@gmail.com>]

On Fri, Jul 27, 2012 at 11:04:02AM +0200, Lukáš Czerner wrote:
> Add Zheng Liu to the CC

Hi Lukas,

It looks good to me. :-)

Regards,
Zheng

> 
> On Fri, 27 Jul 2012, Lukas Czerner wrote:
> 
> > Date: Fri, 27 Jul 2012 10:01:06 +0200
> > From: Lukas Czerner <lczerner@redhat.com>
> > To: linux-fsdevel@vger.kernel.org
> > Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, hughd@google.com,
> >     linux-mmc@vger.kernel.org, Lukas Czerner <lczerner@redhat.com>
> > Subject: [PATCH 07/15] ext4: Take i_mutex before punching hole
> > 
> > Currently the allocation might happen in the punched range after the
> > truncation and before the releasing the space of the range. This would
> > lead to blocks being unallocated under the mapped buffer heads resulting
> > in nasty bugs.
> > 
> > With this commit we take i_mutex before going to do anything in the
> > ext4_ext_punch_hole() preventing any write to happen while the hole
> > punching is in progress. This will also allow us to ditch the writeout
> > of dirty pages withing the range.
> > 
> > This commit was based on code provided by Zheng Liu, thanks!
> > 
> > Signed-off-by: Lukas Czerner <lczerner@redhat.com>
> > ---
> >  fs/ext4/extents.c |   26 ++++++++++----------------
> >  1 files changed, 10 insertions(+), 16 deletions(-)
> > 
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 91341ec..2d6a216 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -4755,9 +4755,11 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
> >  	loff_t first_page_offset, last_page_offset;
> >  	int credits, err = 0;
> >  
> > +	mutex_lock(&inode->i_mutex);
> > +
> >  	/* No need to punch hole beyond i_size */
> >  	if (offset >= inode->i_size)
> > -		return 0;
> > +		goto out1;
> >  
> >  	/*
> >  	 * If the hole extends beyond i_size, set the hole
> > @@ -4775,18 +4777,6 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
> >  	first_page_offset = first_page << PAGE_CACHE_SHIFT;
> >  	last_page_offset = last_page << PAGE_CACHE_SHIFT;
> >  
> > -	/*
> > -	 * Write out all dirty pages to avoid race conditions
> > -	 * Then release them.
> > -	 */
> > -	if (mapping->nrpages && mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
> > -		err = filemap_write_and_wait_range(mapping,
> > -			offset, offset + length - 1);
> > -
> > -		if (err)
> > -			return err;
> > -	}
> > -
> >  	/* Now release the pages */
> >  	if (last_page_offset > first_page_offset) {
> >  		truncate_pagecache_range(inode, first_page_offset,
> > @@ -4798,12 +4788,14 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
> >  
> >  	credits = ext4_writepage_trans_blocks(inode);
> >  	handle = ext4_journal_start(inode, credits);
> > -	if (IS_ERR(handle))
> > -		return PTR_ERR(handle);
> > +	if (IS_ERR(handle)) {
> > +		err = PTR_ERR(handle);
> > +		goto out1;
> > +	}
> >  
> >  	err = ext4_orphan_add(handle, inode);
> >  	if (err)
> > -		goto out;
> > +		goto out1;
> >  
> >  	/*
> >  	 * Now we need to zero out the non-page-aligned data in the
> > @@ -4893,6 +4885,8 @@ out:
> >  	inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
> >  	ext4_mark_inode_dirty(handle, inode);
> >  	ext4_journal_stop(handle);
> > +out1:
> > +	mutex_unlock(&inode->i_mutex);
> >  	return err;
> >  }
> >  int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> > 
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