fs/buffer.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/fs/buffer.c b/fs/buffer.c
index 3586fb05c8ce..c4e11390a44c 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2893,6 +2893,55 @@ static void end_bio_bh_io_sync(struct bio *bio, int err)
 	bio_put(bio);
 }
 
+/*
+ * This allows us to do IO even on the odd last sectors
+ * of a device, even if the bh block size is some multiple
+ * of the physical sector size.
+ *
+ * We'll just truncate the bio to the size of the device,
+ * and clear the end of the buffer head manually.
+ *
+ * Truly out-of-range accesses will turn into actual IO
+ * errors, this only handles the "we need to be able to
+ * do IO at the final sector" case.
+ */
+static void guard_bh_eod(int rw, struct bio *bio, struct buffer_head *bh)
+{
+	sector_t maxsector;
+	unsigned bytes;
+
+	maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
+	if (!maxsector)
+		return;
+
+	/*
+	 * If the *whole* IO is past the end of the device,
+	 * let it through, and the IO layer will turn it into
+	 * an EIO.
+	 */
+	if (unlikely(bio->bi_sector >= maxsector))
+		return;
+
+	maxsector -= bio->bi_sector;
+	bytes = bio->bi_size;
+	if (likely((bytes >> 9) <= maxsector))
+		return;
+
+	/* Uhhuh. We've got a bh that straddles the device size! */
+	bytes = maxsector << 9;
+
+	/* Truncate the bio.. */
+	bio->bi_size = bytes;
+	bio->bi_io_vec[0].bv_len = bytes;
+
+	/* ..and clear the end of the buffer for reads */
+	if (rw & READ) {
+		void *kaddr = kmap_atomic(bh->b_page);
+		memset(kaddr + bh_offset(bh) + bytes, 0, bh->b_size - bytes);
+		kunmap_atomic(kaddr);
+	}
+}
+
 int submit_bh(int rw, struct buffer_head * bh)
 {
 	struct bio *bio;
@@ -2929,6 +2978,9 @@ int submit_bh(int rw, struct buffer_head * bh)
 	bio->bi_end_io = end_bio_bh_io_sync;
 	bio->bi_private = bh;
 
+	/* Take care of bh's that straddle the end of the device */
+	guard_bh_eod(rw, bio, bh);
+
 	bio_get(bio);
 	submit_bio(rw, bio);