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From:   John Hubbard <jhubbard@nvidia.com>
To:     Jens Axboe <axboe@kernel.dk>, Jan Kara <jack@suse.cz>,
        Christoph Hellwig <hch@infradead.org>,
        Dave Chinner <dchinner@redhat.com>,
        "Darrick J . Wong" <djwong@kernel.org>,
        Theodore Ts'o <tytso@mit.edu>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Chaitanya Kulkarni <kch@nvidia.com>
CC:     <linux-block@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
        <linux-xfs@vger.kernel.org>, <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        John Hubbard <jhubbard@nvidia.com>
Subject: [RFC PATCH 3/7] block, fs: assert that key paths use iovecs, and nothing else
Date:   Fri, 25 Feb 2022 00:50:21 -0800
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Upcoming changes to Direct IO will change it from acquiring pages via
get_user_pages_fast(), to calling pin_user_pages_fast() instead.

Place a few assertions at key points, that the pages are IOVEC (user
pages), to enforce the assumptions that there are no kernel or pipe or
other odd variations being passed.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 block/bio.c    | 4 ++++
 fs/direct-io.c | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/block/bio.c b/block/bio.c
index b15f5466ce08..4679d6539e2d 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1167,6 +1167,8 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
 	pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
 
+	WARN_ON_ONCE(!iter_is_iovec(iter));
+
 	size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
 	if (unlikely(size <= 0))
 		return size ? size : -EFAULT;
@@ -1217,6 +1219,8 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter)
 	BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
 	pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
 
+	WARN_ON_ONCE(!iter_is_iovec(iter));
+
 	size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
 	if (unlikely(size <= 0))
 		return size ? size : -EFAULT;
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 38bca4980a1c..7dbbbfef300d 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -169,6 +169,8 @@ static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
 {
 	ssize_t ret;
 
+	WARN_ON_ONCE(!iter_is_iovec(sdio->iter));
+
 	ret = iov_iter_get_pages(sdio->iter, dio->pages, LONG_MAX, DIO_PAGES,
 				&sdio->from);
 
-- 
2.35.1