linux-kernel - Re: 2.6.24-rc2-mm1

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Date:	Thu, 15 Nov 2007 16:14:07 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Jiri Kosina <jikos@...os.cz>, Greg KH <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.24-rc2-mm1

On Thu, Nov 15, 2007 at 03:38:13AM +0100, Kay Sievers wrote:
> On Thu, 2007-11-15 at 09:01 +0800, Dave Young wrote:
> > On Nov 15, 2007 5:27 AM, Kay Sievers <kay.sievers@...y.org> wrote:
> > > On Wed, 2007-11-14 at 20:19 +0100, Jiri Kosina wrote:
> > > > On Wed, 14 Nov 2007, Kay Sievers wrote:
> > > >
> > > > > Could it be an init-order problem, where something tries to use the
> > > > > block subsystem? Before it is initialized with:
> > > > >   block/genhd.c :: subsys_initcall(genhd_device_init);
> > > > > If that's the case, we have an old bug that nobody noticed with static
> > > > > structures, which are zeroed that time, but definitely not properly
> > > > > initialized. I'll try to build loop non-modular now, and see if that
> > > > > makes the bug appear here.
> > >
> > > > my .config with which I reproduc this on 2.6.24-rc2-mm1 reliably can be
> > > > obtained from http://www.jikos.cz/jikos/junk/.config
> > >
> > > Hmm, that config doesn't do anything here, and if I make it boot, it
> > > does not show the bug.
> > >
> > > Could you possibly enable kobject debugging and see if that exposes
> > > something, maybe something goes wrong with the kset refcount and it gets
> > > released while in use.
> > >
> > Hi,
> > I would do that.
> 
> That would be great.
> 
> > BTW, The bug report as EIP  at __list_add with CONFIG_DEBUG_LIST=y
> 
> Yeah, that hints that the kset, which contains the list, is not
> allocated at the time it is used, or it is already released (kfree)
> again by some buggy logic.
Yes, I debugged it, there's some new findings.
It is freed by put_disk.
The floppy driver alloc_disk and then call put_disk without register_disk.
in kobject_cleanup line 551:
if(s)
	kset_put(s);
Now the kset is set in alloc_disk after kobject_init, so it is not refereced yet.
please try this patch:
 
block/genhd.c |    2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff -upr linux/block/genhd.c linux.new/block/genhd.c
--- linux/block/genhd.c	2007-11-15 15:59:11.000000000 +0800
+++ linux.new/block/genhd.c	2007-11-15 15:59:39.000000000 +0800
@@ -718,9 +718,9 @@ struct gendisk *alloc_disk_node(int mino
 			}
 		}
 		disk->minors = minors;
-		kobject_init(&disk->kobj);
 		disk->kobj.kset = block_kset;
 		disk->kobj.ktype = &ktype_block;
+		kobject_init(&disk->kobj);
 		rand_initialize_disk(disk);
 		INIT_WORK(&disk->async_notify,
 			media_change_notify_thread);
-
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