linux-kernel - Re: [PATCH 1/1] block: initialise bd

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Message-ID: <4E0CD89D.3080001@sandeen.net>
Date:	Thu, 30 Jun 2011 15:12:13 -0500
From:	Eric Sandeen <sandeen@...deen.net>
To:	Lachlan McIlroy <lmcilroy@...hat.com>
CC:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] block: initialise bd_super in bdget()

On 6/29/11 8:01 PM, Lachlan McIlroy wrote:
> bd_super is currently reset to NULL in kill_block_super() so we rely on previous
> users of the block_device object to initialise this value for the next user.
> This quirk was exposed on RHEL5 when a third party filesystem did not always use
> kill_block_super() and therefore bd_super wasn't being reset when a block_device
> object was recycled within the cache.  This may not be a problem upstream but
> makes sense to be defensive.
> 
> Signed-off-by: Lachlan McIlroy <lmcilroy@...hat.com>
> ---

This seems reasonable to me, I think it's dangerous to assume the prior user
will "put it away" properly.

blkdev_releasepage() then may try to deref it and go boom, without this
explicit initialization.

And there is already other initialization in bdget()...

Reviewed-by: Eric Sandeen <sandeen@...hat.com>

>  fs/block_dev.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 610e8e0..2b0dc33 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -547,6 +547,7 @@ struct block_device *bdget(dev_t dev)
>  
>  	if (inode->i_state & I_NEW) {
>  		bdev->bd_contains = NULL;
> +		bdev->bd_super = NULL;
>  		bdev->bd_inode = inode;
>  		bdev->bd_block_size = (1 << inode->i_blkbits);
>  		bdev->bd_part_count = 0;

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