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

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Date:	Mon, 11 Jan 2010 19:00:00 +0100
From:	Jan Kara <jack@...e.cz>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Jan Kara <jack@...e.cz>, 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

On Mon 11-01-10 11:53:19, Eric Sandeen wrote:
> 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?
  No, you are exactly right (sadly). Linus already has a pull request with
the fix in his mailbox.
  The fix is attached if you need it for something.


									Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR

View attachment "0001-quota-Fix-dquot_transfer-for-filesystems-different-f.patch" of type "text/x-patch" (1243 bytes)