lkml.org 
[lkml]   [2000]   [Sep]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Bugfix in dquot_transfer()


On Thu, 14 Sep 2000, Jan Kara wrote:

> > > of blocks after notify_change() once more all the quota will be counted
> > > properly. The only problem is that quota can be exceeded this way. We have to check
> >
> > Nope. You've just shifted the race window (and inverted the
> > effect) - think what happens if you've got new allocations after the UID
> > change but before the return from notify_change().
> Quota will be still acounted to old user - it's independent of i_uid contents -
> so when we switch pointers to dquot structures and move allocated space without
> blocking there shouldn't be problem...

You still have a window when i_blocks is out of sync with
dquot. If your nice, non-blocking, etc. switch happens in that window - we
are toast, right? It means that we can't change i_blocks before dquot -
currently dquot_{alloc,free}_block() can block. Now, consider the
following:

dquot_transfer()
....
switched
dqput() ****BLOCKED
dquot_alloc_block()
dqduplicate()
dquot_lock() **** BLOCKED
dquot_unlock()
dqput()
....
finished

....
updated the thing *** WINDOW OPENED
dquot_unlock()
dqput() **** BLOCKED
another dquot_transfer()
....
switched
....
finished
finished

updated i_blocks *** WINDOW CLOSED

The second switch happens in the window. QED.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 12:38    [W:0.073 / U:0.816 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site