linux-ext4 - Re: [PATCH 2/2 V2] ext4: don't bump nr_to_write if LONG

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Date:	Fri, 03 Sep 2010 16:37:48 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/2 V2] ext4: don't bump nr_to_write if LONG_MAX

Eric Sandeen wrote:
> In some cases we can reach ext4_da_writepages() with
> wbc->nr_to_write == LONG_MAX, !range_cyclic, and range_whole=1;
> in this case we will try to bump it up by a factor of 8, which
> leads to a desired_nr_to_write value of -8.

Sorry Ted, hold off on this, it should have been LLONG_MAX of course,
and I'm still looking for one other bit of brokennes I see.

The 1/2 patch should be good though.

-Eric

> We still get through the logic without actually changing
> wbc->nr_to_write because the other tests which would change
> it don't trip due to the negative value, but it seems dangerous
> to overflow  desired_nr_to_write in the interim, it's not an 
> obvious situation.
> 
> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
> ---
> 
> (V2 minor commit message edits)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 93497f6..2e72a4a 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3004,9 +3004,11 @@ static int ext4_da_writepages(struct address_space *mapping,
>  	 * sbi->max_writeback_mb_bump whichever is smaller.
>  	 */
>  	max_pages = sbi->s_max_writeback_mb_bump << (20 - PAGE_CACHE_SHIFT);
> -	if (!range_cyclic && range_whole)
> -		desired_nr_to_write = wbc->nr_to_write * 8;
> -	else
> +	if (!range_cyclic && range_whole) {
> +		desired_nr_to_write = wbc->nr_to_write;
> +		if (desired_nr_to_write != LONG_MAX)
> +			desired_nr_to_write *= 8;
> +	} else
>  		desired_nr_to_write = ext4_num_dirty_pages(inode, index,
>  							   max_pages);
>  	if (desired_nr_to_write > max_pages)
> 
> 
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