From 17d51b10d7773e4618bcac64648f30f12d4078fb Mon Sep 17 00:00:00 2001 From: Martin Wilck Date: Wed, 25 Jul 2018 23:15:09 +0200 Subject: [PATCH] block: bio_iov_iter_get_pages: pin more pages for multi-segment IOs bio_iov_iter_get_pages() currently only adds pages for the next non-zero segment from the iov_iter to the bio. That's suboptimal for callers, which typically try to pin as many pages as fit into the bio. This patch converts the current bio_iov_iter_get_pages() into a static helper, and introduces a new helper that allocates as many pages as 1) fit into the bio, 2) are present in the iov_iter, 3) and can be pinned by MM. Error is returned only if zero pages could be pinned. Because of 3), a zero return value doesn't necessarily mean all pages have been pinned. Callers that have to pin every page in the iov_iter must still call this function in a loop (this is currently the case). This change matters most for __blkdev_direct_IO_simple(), which calls bio_iov_iter_get_pages() only once. If it obtains less pages than requested, it returns a "short write" or "short read", and __generic_file_write_iter() falls back to buffered writes, which may lead to data corruption. Fixes: 72ecad22d9f1 ("block: support a full bio worth of IO for simplified bdev direct-io") Reviewed-by: Christoph Hellwig Signed-off-by: Martin Wilck Signed-off-by: Jens Axboe --- block/bio.c | 35 ++++++++++++++++++++++++++++++++--- 1 file changed, 32 insertions(+), 3 deletions(-) diff --git a/block/bio.c b/block/bio.c index cd55ea6bd47c..dc07a427e782 100644 --- a/block/bio.c +++ b/block/bio.c @@ -903,14 +903,16 @@ int bio_add_page(struct bio *bio, struct page *page, EXPORT_SYMBOL(bio_add_page); /** - * bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio + * __bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio * @bio: bio to add pages to * @iter: iov iterator describing the region to be mapped * - * Pins as many pages from *iter and appends them to @bio's bvec array. The + * Pins pages from *iter and appends them to @bio's bvec array. The * pages will have to be released using put_page() when done. + * For multi-segment *iter, this function only adds pages from the + * the next non-empty segment of the iov iterator. */ -int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) +static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) { unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt, idx; struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt; @@ -947,6 +949,33 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) iov_iter_advance(iter, size); return 0; } + +/** + * bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio + * @bio: bio to add pages to + * @iter: iov iterator describing the region to be mapped + * + * Pins pages from *iter and appends them to @bio's bvec array. The + * pages will have to be released using put_page() when done. + * The function tries, but does not guarantee, to pin as many pages as + * fit into the bio, or are requested in *iter, whatever is smaller. + * If MM encounters an error pinning the requested pages, it stops. + * Error is returned only if 0 pages could be pinned. + */ +int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) +{ + unsigned short orig_vcnt = bio->bi_vcnt; + + do { + int ret = __bio_iov_iter_get_pages(bio, iter); + + if (unlikely(ret)) + return bio->bi_vcnt > orig_vcnt ? 0 : ret; + + } while (iov_iter_count(iter) && !bio_full(bio)); + + return 0; +} EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages); static void submit_bio_wait_endio(struct bio *bio) -- GitLab