Date:	Thu, 03 Jul 2008 10:38:40 -0700
From:	Mingming Cao <cmm@...ibm.com>
To:	Aneesh Kumar <aneesh.kumar@...il.com>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: Gentoo with ext4-patch-queue snapshots


在 2008-07-03四的 19:37 +0530，Aneesh Kumar写道：
> [sending via gmail  ]
> 
> On Thu, Jul 03, 2008 at 05:03:25PM +0530, Aneesh Kumar K.V wrote:
> > On Wed, Jul 02, 2008 at 10:19:54AM -0700, Mingming Cao wrote:
> > >
> > > On Tue, 2008-07-01 at 17:50 +0000, Gary Hawco wrote:
> > > > Mingming,
> > > >
> > > > Can you post that patch somewhere for download? I access my email using
> > > > Windows Vista, not in linux, so it would be very laborious to hand copy
> > > > this patch and recreate it in linux.
> > > >
> > > Patch attached.
> > >
> > > > Updated the 2.6.26-rc8 kernel with the latest snapshot from today at
> > > > 1833hrs GMT. All hell broke loose in Gentoo, The new kernel wouldn't allow
> > > > the system to remount read/write on boot.  But it worked fine in Slackware.
> > > > Gentoo with the experimental openrc-0.2.5 and baselayout2 apparently does
> > > > not like ext4.
> > > >
> > >
> >
> > I think we need to protect i_disksize update with i_data_sem. Otherwise
> > a parallel writepages and write_end can cause issues. I guess that is
> > what Gary is finding. I also did some cleanup for the patch
> >
> 
> better one moving ext4_truncate i_disksize update under i_data_sem.
> ext4_ext_truncate is already doing this.
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index fcaafe4..05e9790 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -1893,18 +1893,29 @@ static int ext4_da_write_begin(struct file
> *file, struct address_space *mapping,
>  /*
>   * Check if we should update i_disksize
>   * when write to the end of file but not require block allocation
> + * We check only the buffer head mapping the offset.
> + * ex: File with blocksize 1K page size 4K
> + * block 1 and 2 are holes, block 3 is mapped and half filled
> + * seek to block 1 and write ( marked the buffer delay )
> + * seek to block 3 and extent the end of file with end of file still
> + * falling within block 3. Here the writepages won't update the i_disksize
> + * properly because it allocate only block 1. So we need to update
> + * i_disksize in write_end checking only the offset
> + *
>   */

Okay, Iwill add this comment

> -static int ext4_da_should_update_i_disksize(struct page *page,
> -					 unsigned long offset)
> +static int ext4_da_should_update_i_disksize(struct address_space *mapping,
> +					struct page *page, unsigned long offset)
>  {
> -	struct buffer_head *bh;
> -	unsigned int idx;
>  	int i;
> +	unsigned int idx;
> +	struct buffer_head *bh;
> +	struct inode *inode = mapping->host;
> +	unsigned blocksize = inode->i_sb->s_blocksize;
> 
We could use page->mapping->host to get the inode pointer, so no need to
pass the mapping pointer. But I am fine with this.

>  	bh = page_buffers(page);
> -	idx = offset/bh->b_size;
> +	idx = (offset + blocksize - 1)/blocksize;
> 
> -	for (i=0; i < idx; i++)
> +	for (i = 1; i < idx; i++)
>  		bh = bh->b_this_page;
> 
Ack

>  	if (!buffer_mapped(bh) || (buffer_delay(bh)))
> @@ -1934,15 +1945,20 @@ static int ext4_da_write_end(struct file *file,
> 
>  	new_i_size = pos + copied;
>  	if (new_i_size > EXT4_I(inode)->i_disksize)
> -		if (ext4_da_should_update_i_disksize(page, end)) {
> +		if (ext4_da_should_update_i_disksize(mapping, page, end)) {
>  			/*
>  			 * Updating i_disksize when extending file without
>  			 * need block allocation
>  			 */
> -			if (ext4_should_order_data(inode))
> -				ret = ext4_jbd2_file_inode(handle, inode);
> +			down_write(&EXT4_I(inode)->i_data_sem);
> +			if (new_i_size > EXT4_I(inode)->i_disksize) {
> +				if (ext4_should_order_data(inode))
> +					ret = ext4_jbd2_file_inode(handle,
> +									inode);
> 
> -			EXT4_I(inode)->i_disksize = new_i_size;
> +				EXT4_I(inode)->i_disksize = new_i_size;
> +			}
> +			up_write(&EXT4_I(inode)->i_data_sem);
>  		}
>  	ret2 = generic_write_end(file, mapping, pos, len, copied,
>  							page, fsdata);
> @@ -2987,6 +3003,11 @@ void ext4_truncate(struct inode *inode)
>  	 */
>  	if (ext4_orphan_add(handle, inode))
>  		goto out_stop;
> +	/*
> +	 * From here we block out all ext4_get_block() callers who want to
> +	 * modify the block allocation tree.
> +	 */
> +	down_write(&ei->i_data_sem);
> 
>  	/*
>  	 * The orphan list entry will now protect us from any crash which
> @@ -2997,12 +3018,6 @@ void ext4_truncate(struct inode *inode)
>  	 */
>  	ei->i_disksize = inode->i_size;
> 
> -	/*
> -	 * From here we block out all ext4_get_block() callers who want to
> -	 * modify the block allocation tree.
> -	 */
> -	down_write(&ei->i_data_sem);
> -
>  	if (n == 1) {		/* direct blocks */
>  		ext4_free_data(handle, inode, NULL, i_data+offsets[0],
>  			       i_data + EXT4_NDIR_BLOCKS);
> 

Ack.

I will merge the update to the parent patch, thanx

Mingming
> -aneesh
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