Re: [PATCH] btrfs: fix write_dev_supers

[Chris Mason <chris.mason@oracle.com>]

On Tue, Jun 09, 2009 at 10:46:55AM +0900, Hisashi Hifumi wrote:
> Hi.
> 
> I got following BUG trace.
> This is violation of BUG_ON(!buffer_locked(bh)) check on submit_bh() function.
> In write_dev_supers(), if wait parameter is set and buffer_uptodate() check
> is negative,  submit_bh() is executed and hit above BUG_ON.
> So I fixed this issue.

Thanks for finding this bug and sending the patch.

This function is very confusing.  If wait parameter is set, it
isn't supposed to do any IO at all.  The caller first does
write_dev_supers with wait == 0, and that sends all the supers down on
all the devices.

Then it calls again with wait == 1, which is supposed to make sure all
the supers actually got to disk.

We should change the wait == 0 behavior to leave a reference held on all
the buffers, and wait == 1 to drop that reference.  That way the buffer
won't disappear while we are waiting, and we can return an error if the
buffer wasn't up to date when wait == 1.

Are you interested in fixing this?

-chris