lkml.org 
[lkml]   [2008]   [Nov]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/2] md: make devices disappear when they are no longer needed.
On Mon, Nov 24, 2008 at 02:55:30PM +1100, NeilBrown wrote:
> Between the call
> __blkdev_get->get_gendisk->kobj_lookup->md_probe
> and the call
> __blkdev_get->md_open
>
> there is no obvious way to hold a reference on the mddev any more, so
> unless something is done, it will disappear and gendisk will be
> destroyed prematurely.
>
> Also, once we decide to destroy the mddev, there will be an unlockable
> moment before the gendisk is unlinked (blk_unregister_region) during
> which a new reference to the gendisk can be created. We need to
> ensure that this reference can not be used. i.e. the ->open must
> fail.
>
> So:
> 1/ in md_probe we set a flag in the mddev (hold_active) which
> indicates that the array should be treated as active, even
> though there are no references, and no appearance of activity.
> This is cleared by md_release when the device is closed.
> This ensure that the gendisk will survive between md_probe and
> md_open.

That won't work. Note that you are not guaranteed that md_release() will be
called after md_probe(); there are failure exits in __blkdev_get() that do
not reach ->open() at all.

What lifetime rules do you really want? I never liked the tricks pulled
by md wrt gendisk lifetimes and that might be a good time to sort that
out for good...

What should happen to things like pending IO, etc. on array destruction?
AFAICS, that's the real question...


\
 
 \ /
  Last update: 2008-11-24 05:27    [W:0.075 / U:0.944 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site