linux-kernel - Re: [PATCH] vfs: calculate block-size correctly

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Message-Id: <20100913160905.332ff633.akpm@linux-foundation.org>
Date:	Mon, 13 Sep 2010 16:09:05 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cong Meng <mcpacino@...il.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@....de>,
	Nick Piggin <npiggin@...nel.dk>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfs: calculate block-size correctly

On Wed, 8 Sep 2010 18:07:10 +0800
Cong Meng <mcpacino@...il.com> wrote:

> I sent this patch half mount ago, but no response at all. If anything is
> wrong, please tell me. Thanks a lots. This is my first time to send patch
> to linux kernel.
> 
> The invocation of __getblk(bdev, block, size) will cause kernel stall if
> the @size parameter is not equal to the blockr-size of @bdev, which is saved
> in bdev->bd_inode->i_blkbits.
> 
> submit_bh() has the similar problem.
> 
> This patch calculates the block-size using i_blkbits.
> So that, for example, __getblk() can get a 4K buffer head while the
> block-size of @bdev is 1K.
> 

This comes up every couple of years and iirc we always decided that
it's a bug in the calling code somewhere.  How did you hit it?


> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1051,10 +1051,7 @@ grow_buffers(struct block_device *bdev, sector_t block, int size)
>  	pgoff_t index;
>  	int sizebits;
>  
> -	sizebits = -1;
> -	do {
> -		sizebits++;
> -	} while ((size << sizebits) < PAGE_SIZE);

I'm sure the existing code could use __roundup_pow_of_two() here.

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