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Date:   Thu, 30 Jun 2022 20:07:24 -0600
From:   Keith Busch <kbusch@kernel.org>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
        Matthew Wilcox <willy@infradead.org>,
        David Howells <dhowells@redhat.com>,
        Dominique Martinet <asmadeus@codewreck.org>,
        Christian Brauner <brauner@kernel.org>,
        linux-fsdevel@vger.kernel.org
Subject: Re: [block.git conflicts] Re: [PATCH 37/44] block: convert to
 advancing variants of iov_iter_get_pages{,_alloc}()
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On Thu, Jun 30, 2022 at 11:39:36PM +0100, Al Viro wrote:
> On Thu, Jun 30, 2022 at 11:11:27PM +0100, Al Viro wrote:
> 
> > ... and the first half of that thing conflicts with "block: relax direct
> > io memory alignment" in -next...
> 
> BTW, looking at that commit - are you sure that bio_put_pages() on failure
> exit will do the right thing?  We have grabbed a bunch of page references;
> the amount if DIV_ROUND_UP(offset + size, PAGE_SIZE).  And that's before
> your
>                 size = ALIGN_DOWN(size, bdev_logical_block_size(bio->bi_bdev));

Thanks for the catch, it does look like a page reference could get leaked here.

> in there.  IMO the following would be more obviously correct:
>         size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
>         if (unlikely(size <= 0))
>                 return size ? size : -EFAULT;
> 
> 	nr_pages = DIV_ROUND_UP(size + offset, PAGE_SIZE);
> 	size = ALIGN_DOWN(size, bdev_logical_block_size(bio->bi_bdev));
> 
>         for (left = size, i = 0; left > 0; left -= len, i++) {
> ...
>                 if (ret) {
> 			while (i < nr_pages)
> 				put_page(pages[i++]);
>                         return ret;
>                 }
> ...
> 
> and get rid of bio_put_pages() entirely.  Objections?


I think that makes sense. I'll give your idea a test run tomorrow.