linux-ext4 - Re: [PATCH -v2 6/6] ext4: use bio layer instead of buffer layer in mpage_da_submit

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Message-ID: <20101025123353.GA16981@thunk.org>
Date:	Mon, 25 Oct 2010 08:33:53 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Dmitry <dmonakhov@...nvz.org>
Cc:	linux-ext4@...r.kernel.org, akpm@...ux-foundation.org,
	axboe@...nel.dk
Subject: Re: [PATCH -v2 6/6] ext4: use bio layer instead of buffer layer in
 mpage_da_submit_io

On Mon, Oct 25, 2010 at 09:16:16AM +0400, Dmitry wrote:
> > +	if (bio) {
> > +		bio_get(io->io_bio);
> > +		submit_bio(io->io_op, io->io_bio);
> > +		BUG_ON(bio_flagged(io->io_bio, BIO_EOPNOTSUPP));
> Definitly this BUG_ON should be converted to ext4_error or something
> similar, otherwhise writeback attempt to removed usb-stick will be fatal
> for a whole system. IMHO it is reasonable to skip this check at all,
> because all work will be done in ext4_end_bio() anyway.
> > +		bio_put(io->io_bio);

Cut and pasted from XFS.  From what I could tell from the block I/O
layer, the only time the buffer I/O layer should return BIO_EOPNOTSUPP
is if we pass it a discard or barrier request, and we're doing neither
here.  So I don't think it should trigger on a removed usb-stick.

At the same time, it's not clear what good the BUG_ON() is doing here,
either.  So perhaps we could could drop the BUG_ON, at which point we
could drop the bio_get() and bio_put() calls, too.  To be honest I'm
not entirely sure why the XFS code does this.

Jens?  Any reason why I shouldn't just remove the bio_get(), the
BUG_ON()check, and bio_put() calls?

					- Ted
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