On Mon, Aug 01, 2011 at 07:47:49AM +0800, Dave Chinner wrote:

On Sun, Jul 31, 2011 at 11:10:14PM +0800, Wu Fengguang wrote:

quoted

On Sat, Jul 30, 2011 at 09:44:22PM +0800, Christoph Hellwig wrote:

quoted

This patch fixes the hang for me.

Thanks. It'd be better to get the _simple and tested_ fix into 3.1-rc1.
(if anyone find major problems with the fix, please speak up)

Yes, I already have, a couple of hours before you sent this:

http://www.spinics.net/lists/linux-fsdevel/msg47357.html

Err I found it in my spam folder.. and added you to the white list :)

We haven't found the root cause of the problem, and writeback cannot
hold off grab_super_passive() because writeback only holds read
locks on s_umount, just like grab_super_passive. So if
grab_super_passive is failing, there is some other, not yet
unidentified actor causing this problem....

Yeah sorry, I totally overlooked the read lock. Since Linus has
pointed out the possibility of read-write-read deadlock, I'll jump
to your more recent email for the root cause.

Thanks,
Fengguang