linux-kernel - Re: [next-20101038] Call trace in ext4

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Date:	Thu, 28 Oct 2010 14:36:08 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Ted Ts'o" <tytso@....edu>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	sedat.dilek@...il.com, LKML <linux-kernel@...r.kernel.org>,
	linux-ext4@...r.kernel.org, sfr@...b.auug.org.au,
	Arnd Bergmann <arnd@...db.de>,
	Avinash Kurup <kurup.avinash@...il.com>
Subject: Re: [next-20101038] Call trace in ext4

Ted Ts'o wrote:
> On Thu, Oct 28, 2010 at 02:01:18PM -0400, Ted Ts'o wrote:
>> On Thu, Oct 28, 2010 at 07:52:21PM +0200, Markus Trippelsdorf wrote:
>>> The same BUG (inode.c:2721) happend here today running latest vanilla
>>> git. There is nothing in my logs unfortunately, but I shot a photo of
>>> the trace (see attachment).
>> I see, it's the page_buffers() call which is triggering.  Looking into
>> it...
> 
> Can folks let me know if this fixes the problem?

Ted, any idea what caused the change in behavior here?

-Eric

> In this case I haven't been able to replicate the problem, but I've
> eyeballed the problem and I'm about 90% certain this should fix
> things.  But I don't want to push this to Linus until I get
> confirmation from you all that it fixes things.  That's just one of
> the ways in which your testing is critically important for ext4, so
> thanks again for your help in the past, present, and future.
> Thanks!!
> 
> 						- Ted
> 
> commit 51279fcb9720aa856ad81673886ca2349a373dac
> Author: Theodore Ts'o <tytso@....edu>
> Date:   Thu Oct 28 15:15:21 2010 -0400
> 
>     ext4: BUG_ON fix: check if page has buffers before calling page_buffers()
>     
>     We need to make check if a page does not have buffes by checking
>     page_has_buffers(page) before calling page_buffers(page) in
>     ext4_writepage().  Otherwise page_buffers() could throw a BUG_ON.
>     
>     Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 2d6c6c8..1916164 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2718,7 +2718,7 @@ static int ext4_writepage(struct page *page,
>  	 * try to create them using __block_write_begin.  If this
>  	 * fails, redirty the page and move on.
>  	 */
> -	if (!page_buffers(page)) {
> +	if (!page_has_buffers(page)) {
>  		if (__block_write_begin(page, 0, len,
>  					noalloc_get_block_write)) {
>  		redirty_page:
> @@ -2732,12 +2732,10 @@ static int ext4_writepage(struct page *page,
>  	if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
>  			      ext4_bh_delay_or_unwritten)) {
>  		/*
> -		 * We don't want to do block allocation So redirty the
> -		 * page and return We may reach here when we do a
> -		 * journal commit via
> -		 * journal_submit_inode_data_buffers.  If we don't
> -		 * have mapping block we just ignore them. We can also
> -		 * reach here via shrink_page_list
> +		 * We don't want to do block allocation, so redirty
> +		 * the page and return.  We may reach here when we do
> +		 * a journal commit via journal_submit_inode_data_buffers.
> +		 * We can also reach here via shrink_page_list
>  		 */
>  		goto redirty_page;
>  	}
> --
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