Re: [Jfs-discussion] Kernel oops when accessing to mounted, but unplugged JFS

[Alexander Kolesen <kolesen.a@gmail.com>]

> On Sun, 2010-11-21 at 18:57 +0100, Andi Kleen wrote:
> > Alexander Kolesen <kolesen.a@gmail.com> writes:
> > 
> > [Rafael, a new regression]
> > 
> > > Hello.
> > > I've built a kernel from
> > > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
> > > (Date:   Fri Nov 19 19:46:45 2010 -0800)
> > > and got a kernel oops when tried to access to unplugged,
> > > but mounted external usb storage formatted with JFS.
> > 
> > Al seems to be the last person who touched it, maybe it's 
> > related to his changes, like this one. 
> > 
> > commit 152a08366671080f27b32e0c411ad620c5f88b57
> > Author: Al Viro <viro@zeniv.linux.org.uk>
> > Date:   Sun Jul 25 00:46:55 2010 +0400
> > 
> >     new helper: mount_bdev()
> > 
> >     ... and switch of the obvious get_sb_bdev() users to ->mount()
> > 
> >     Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> 
> I haven't dug too far into this yet, but I suspect that
> aaead25b954879e1a708ff2f3602f494c18d20b5 is related.
> 
> commit aaead25b954879e1a708ff2f3602f494c18d20b5
> Author: Christoph Hellwig <hch@lst.de>
> Date:   Mon Oct 4 14:25:33 2010 +0200
> 
>     writeback: always use sb->s_bdi for writeback purposes
> 
> I'll have to look at what happens when a device is unplugged to see if
> JFS is missing something, or it's more of a generic problem.  I'm open
> to suggestions from anybody on cc.
> 
> Thanks,
> Shaggy
>

I've tested kernel before and after this commit. Yes, it reproduced after,
and didn't reproduced before.

> > 
> > >  
> > > Steps to reproduce:
> > >  mkfs.jfs /dev/sdb1 (unpluggable USB hard drive)
> > >  mount /dev/sdb1 /mnt/drive
> > >  cd /mnt/drive
> > >  touch test
> > >  sync
> > >  ..unplug a drive
> > >  ls
> > >   
> > >
> > > Result:
> > >    BUG: unable to handle kernel NULL pointer dereference at
> > >    0000000000000020
> > >    IP: __mark_inode_dirty
> > >
> > > Then I got a kernel coredump. Here is a stack trace:
> > >
> > > (gdb) bt
> > > #0  __mark_inode_dirty (inode=0xffff880078fc1490, flags=<value optimized out>) at fs/fs-writeback.c:990
> > > #1  0xffffffff810e4990 in mark_inode_dirty_sync (mnt=0xffff88007862fd00, dentry=<value optimized out>) at include/linux/fs.h:1687
> > > #2  touch_atime (mnt=0xffff88007862fd00, dentry=<value optimized out>) at fs/inode.c:1505
> > > #3  0xffffffff810dfeb4 in file_accessed (file=0xffff88006afed600, filler=0xffffffff810dfcf8 <filldir>, buf=0xffff88007762bf38) at include/linux/fs.h:1763
> > > #4  vfs_readdir (file=0xffff88006afed600, filler=0xffffffff810dfcf8 <filldir>, buf=0xffff88007762bf38) at fs/readdir.c:41
> > > #5  0xffffffff810e001a in sys_getdents (fd=<value optimized out>, dirent=0x1f61468, count=32768) at fs/readdir.c:214
> > > #6  0xffffffff810279ab in ?? () at arch/x86/kernel/entry_64.S:479
> > > #7  0x00007f8b23d1a4c5 in ?? ()
> > > #8  0x00000000000002bb in ?? ()
> > > #9  0x0000000000000000 in ?? ()
> > >
> > > (gdb) p bdi
> > > $1 = (struct backing_dev_info *) 0x0
> > >
> > > (gdb) p inode->i_mapping->backing_dev_info 
> > > $15 = (struct backing_dev_info *) 0xffff880078878d48
> > >
> > > (gdb) p inode->i_sb->s_bdi
> > > $16 = (struct backing_dev_info *) 0x0
> > >
> > >
> > > I can't do git bisect because on n'th step my system became unbootable. 
> > > But 2.6.35 doesn't fall.
> -- 
> Dave Kleikamp
> IBM Linux Technology Center
>