linux-ext4 - Re: [PATCH 2/5] quota: decouple fs reserved space from quota reservation

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Date:	Mon, 11 Jan 2010 11:53:19 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Jan Kara <jack@...e.cz>
CC:	stable@...nel.org, linux-ext4@...r.kernel.org, tytso@....edu,
	Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: Re: [PATCH 2/5] quota: decouple fs reserved space from quota reservation

Jan Kara wrote:
> From: Dmitry Monakhov <dmonakhov@...nvz.org>
> 
> Currently inode_reservation is managed by fs itself and this
> reservation is transfered on dquot_transfer(). This means what
> inode_reservation must always be in sync with
> dquot->dq_dqb.dqb_rsvspace. Otherwise dquot_transfer() will result
> in incorrect quota(WARN_ON in dquot_claim_reserved_space() will be
> triggered)
> This is not easy because of complex locking order issues
> for example http://bugzilla.kernel.org/show_bug.cgi?id=14739
> 
> The patch introduce quota reservation field for each fs-inode
> (fs specific inode is used in order to prevent bloating generic
> vfs inode). This reservation is managed by quota code internally
> similar to i_blocks/i_bytes and may not be always in sync with
> internal fs reservation.
> 
> Also perform some code rearrangement:
> - Unify dquot_reserve_space() and dquot_reserve_space()
> - Unify dquot_release_reserved_space() and dquot_free_space()
> - Also this patch add missing warning update to release_rsv()
>   dquot_release_reserved_space() must call flush_warnings() as
>   dquot_free_space() does.
> 
> Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
> Signed-off-by: Jan Kara <jack@...e.cz>
> ---

...

> @@ -1734,7 +1761,7 @@ int dquot_transfer(struct inode *inode, struct
iattr *iattr)
>  	}
>  	spin_lock(&dq_data_lock);
>  	cur_space = inode_get_bytes(inode);
> -	rsv_space = dquot_get_reserved_space(inode);
> +	rsv_space = inode_get_rsv_space(inode);
>  	space = cur_space + rsv_space;
>  	/* Build the transfer_from list and check the limits */
>  	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {

...

>  /*
> + * inode_reserved_space is managed internally by quota, and protected by
> + * i_lock similar to i_blocks+i_bytes.
> + */
> +static qsize_t *inode_reserved_space(struct inode * inode)
> +{
> +	/* Filesystem must explicitly define it's own method in order to use
> +	 * quota reservation interface */
> +	BUG_ON(!inode->i_sb->dq_op->get_reserved_space);

Unless I'm missing something, this just broke quota for everyone
except ext4 ...

sys_chown
	...
		dquot_transfer
			inode_get_rsv_space
				inode_reserved_space

will BUG_ON ext3, we get there with (rightly) no ->get_reserved_space.

Or am I missing something?

-Eric
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