From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp2.provo.novell.com ([137.65.250.81]:48493 "EHLO smtp2.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725777AbeGSK0D (ORCPT ); Thu, 19 Jul 2018 06:26:03 -0400 From: Martin Wilck To: Jens Axboe , Ming Lei , Jan Kara Cc: Hannes Reinecke , Johannes Thumshirn , Kent Overstreet , Christoph Hellwig , linux-block@vger.kernel.org, Martin Wilck Subject: [PATCH 2/2] blkdev: __blkdev_direct_IO_simple: make sure to fill up the bio Date: Thu, 19 Jul 2018 11:39:18 +0200 Message-Id: <20180719093918.28876-3-mwilck@suse.com> In-Reply-To: <20180719093918.28876-1-mwilck@suse.com> References: <20180718075440.GA15254@ming.t460p> <20180719093918.28876-1-mwilck@suse.com> Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org bio_iov_iter_get_pages() returns only pages for a single non-empty segment of the input iov_iter's iovec. This may be much less than the number of pages __blkdev_direct_IO_simple() is supposed to process. Call bio_iov_iter_get_pages() repeatedly until either the requested number of bytes is reached, or bio.bi_io_vec is exhausted. If this is not done, short writes or reads may occur for direct synchronous IOs with multiple iovec slots (such as generated by writev()). In that case, __generic_file_write_iter() falls back to buffered writes, which has been observed to cause data corruption in certain workloads. Note: if segments aren't page-aligned in the input iovec, this patch may result in multiple adjacent slots of the bi_io_vec array to reference the same page (the byte ranges are guaranteed to be disjunct if the preceding patch is applied). We haven't seen problems with that in our and the customer's tests. It'd be possible to detect this situation and merge bi_io_vec slots that refer to the same page, but I prefer to keep it simple for now. Fixes: 72ecad22d9f1 ("block: support a full bio worth of IO for simplified bdev direct-io") Signed-off-by: Martin Wilck --- fs/block_dev.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/fs/block_dev.c b/fs/block_dev.c index 0dd87aa..41643c4 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -221,7 +221,12 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter, ret = bio_iov_iter_get_pages(&bio, iter); if (unlikely(ret)) - return ret; + goto out; + + while (ret == 0 && + bio.bi_vcnt < bio.bi_max_vecs && iov_iter_count(iter) > 0) + ret = bio_iov_iter_get_pages(&bio, iter); + ret = bio.bi_iter.bi_size; if (iov_iter_rw(iter) == READ) { @@ -250,6 +255,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter, put_page(bvec->bv_page); } +out: if (vecs != inline_vecs) kfree(vecs); -- 2.17.1