Re: [PATCH 3/3] block: fix leaking page ref on truncated direct io

[Al Viro <viro@zeniv.linux.org.uk>]

On Tue, Jul 05, 2022 at 08:45:06AM -0700, Keith Busch wrote:
> From: Keith Busch <kbusch@kernel.org>
> 
> The size being added to a bio from an iov is aligned to a block size
> after the pages were gotten. If the new aligned size truncates the last
> page, its reference was being leaked. Ensure all pages that were not
> added to the bio have their reference released.
> 
> Since this essentially requires doing the same that bio_put_pages(), and
> there was only one caller for that function, this patch makes the
> put_page() loop common for everyone.
> 
> Fixes: b1a000d3b8ec5 ("block: relax direct io memory alignment")
> Reported-by: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Keith Busch <kbusch@kernel.org>

I still very much dislike this.  Background: iov_iter_get_pages should
advance the fucking iterator by the amount it has grabbed.  It's
really much cleaner that way.  So your round-down-then-fuck-off-if-zero
is going to be a clumsy.

Whatever; I can deal with that on top of your patch.  Where would you
have it go wrt tree?  Could you do a branch based at the last of your
original series, so that both Jens and I could pull from it?

One thing I would really like to avoid is having the entire #for-5.20/block
in ancestors of those commits; that would make for a monumental headache
with iov_iter series ;-/