linux-kernel - Re: busy inodes -> ext3 umount crash

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Date:	Wed, 21 Apr 2010 17:25:44 -0400
From:	Eric Paris <eparis@...hat.com>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
	adilger@....com, linux-ext4@...r.kernel.org,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	mszeredi@...e.cz
Subject: Re: busy inodes -> ext3 umount crash

On Wed, 2010-04-21 at 17:16 +0200, Jiri Slaby wrote:
> On 04/20/2010 05:28 PM, Jan Kara wrote:
> > On Tue 20-04-10 16:12:03, Jiri Slaby wrote:
> >> On 04/19/2010 04:33 PM, Jiri Slaby wrote:
> >>> The trigger for busy inodes is as simple as (I=initialization done only
> >>> once):
> >>> I> # dd if=/dev/zero of=/dev/shm/ext3 bs=1024 count=1 seek=$((100*1024))
> >>> I> # mkfs.ext3 -m 0 /dev/shm/ext3
> >>> # mount -oloop /dev/shm/ext3 /mnt/c
> >>> # umount /mnt/c
> >>> # dmesg|tail
> >>> VFS: Busy inodes after unmount of loop0. Self-destruct in 5 seconds.
> >>> Have a nice day...
> >>>
> >>> (The printk time varies -- this sequence really suffices.)
> >>
> >> Well, this happens only after gnome-session is started and it's fuzzy --
> >> sometimes it happens, sometimes not. I didn't find 100% trigger yet.
> >   Hmph - maybe something in inotify? Dunno...
> 
> fsnotify...
> 
> >>>> So if you can easily reproduce
> >>>> the "busy inodes" message then I'd start with debugging that one. Do you
> >>>> see it also with vanilla kernels?
> >>
> >> Vanilla seems not to be affected. It's in next/master already though
> >> (2603ecd9). I'll investigate it further later.
> >   Do you mean it's in today's linux-next but not in Linus' tree?
> 
> Yes, exactly.
> 
> And the winner is (seemingly):
> commit 69c1182c4e5d8b7da772ddad512c6f6b67ec1bb8
> Author: Eric Paris <eparis@...hat.com>
> Date:   Thu Dec 17 21:24:27 2009 -0500
> 
>     fsnotify: vfsmount marks generic functions
> 
>     Much like inode-mark.c has all of the code dealing with marks on inodes
>     this patch adds a vfsmount-mark.c which has similar code but is intended
>     for marks on vfsmounts.
> 
>     Signed-off-by: Eric Paris <eparis@...hat.com>

Surprised noone else ever hit this, it's been broken for a LONG time. In
any case I'll have this in the next time he pushes a -next.

-Eric


commit bf770d242d100882891ac60e42f2cf0096fc3f3c
Author: Eric Paris <eparis@...hat.com>
Date:   Wed Apr 21 16:49:38 2010 -0400

    fsnotify: add iput on inodes when no longer marked
    
    fsnotify takes an igrab on an inode when it adds a mark.  The code was
    supposed to drop the reference when the mark was removed.  The problem
    was that what actually happened was below
    
    void fsnotify_destroy_inode_mark(struct fsnotify_mark *mark)
    {
    	...
    	mark->inode = NULL;
    	...
    }
    
    void fsnotify_destroy_mark(struct fsnotify_mark *mark)
    {
    	struct inode *inode = NULL;
    	...
    	if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
    		fsnotify_destroy_inode_mark(mark);
    		inode = mark->i.inode;
    	}
    	...
    	if (inode)
    		iput(inode);
    	...
    }
    
    Obviously the intent was to capture the inode before it was set to NULL in
    fsnotify_destory_inode_mark().
    
    Signed-off-by: Eric Paris <eparis@...hat.com>

diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index 1e824e6..8f3b0e7 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -133,8 +133,8 @@ void fsnotify_destroy_mark(struct fsnotify_mark *mark)
 	spin_lock(&group->mark_lock);
 
 	if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
-		fsnotify_destroy_inode_mark(mark);
 		inode = mark->i.inode;
+		fsnotify_destroy_inode_mark(mark);
 	} else if (mark->flags & FSNOTIFY_MARK_FLAG_VFSMOUNT)
 		fsnotify_destroy_vfsmount_mark(mark);
 	else


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