From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2130.oracle.com ([156.151.31.86]:58502 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725867AbeLAGbM (ORCPT ); Sat, 1 Dec 2018 01:31:12 -0500 Date: Fri, 30 Nov 2018 11:20:47 -0800 From: "Darrick J. Wong" To: Amir Goldstein , Dave Chinner Cc: jencce.kernel@gmail.com, linux-xfs , overlayfs , Zorro Lang , fstests , linux-fsdevel Subject: [RFC PATCH] splice: don't read more than available pipe space Message-ID: <20181130192047.GO8125@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-fsdevel-owner@vger.kernel.org List-ID: From: Darrick J. Wong In commit 4721a601099, we tried to fix a problem wherein directio reads into a splice pipe will bounce EFAULT/EAGAIN all the way out to userspace by simulating a zero-byte short read. This happens because some directio read implementations (xfs) will call bio_iov_iter_get_pages to grab pipe buffer pages and issue asynchronous reads, but as soon as we run out of pipe buffers that _get_pages call returns EFAULT, which the splice code translates to EAGAIN and bounces out to userspace. In that commit, the iomap code catches the EFAULT and simulates a zero-byte read, but that causes assertion errors on regular splice reads because xfs doesn't allow short directio reads. The brokenness is compounded by splice_direct_to_actor immediately bailing on do_splice_to returning <= 0 without ever calling ->actor (which empties out the pipe), so if userspace calls back we'll EFAULT again on the full pipe, and nothing ever gets copied. Therefore, teach splice_direct_to_actor to clamp its requests to the amount of free space in the pipe and remove the simulated short read from the iomap directio code. Fixes: 4721a601099 ("iomap: dio data corruption and spurious errors when pipes fill") Signed-off-by: Darrick J. Wong --- fs/iomap.c | 9 --------- fs/splice.c | 5 ++++- 2 files changed, 4 insertions(+), 10 deletions(-) diff --git a/fs/iomap.c b/fs/iomap.c index 3ffb776fbebe..d6bc98ae8d35 100644 --- a/fs/iomap.c +++ b/fs/iomap.c @@ -1877,15 +1877,6 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, dio->wait_for_completion = true; ret = 0; } - - /* - * Splicing to pipes can fail on a full pipe. We have to - * swallow this to make it look like a short IO - * otherwise the higher splice layers will completely - * mishandle the error and stop moving data. - */ - if (ret == -EFAULT) - ret = 0; break; } pos += ret; diff --git a/fs/splice.c b/fs/splice.c index 3553f1956508..4bd9d9590199 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -949,7 +949,10 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd, size_t read_len; loff_t pos = sd->pos, prev_pos = pos; - ret = do_splice_to(in, &pos, pipe, len, flags); + /* Don't try to read more the pipe has space for. */ + read_len = min_t(size_t, len, + (pipe->buffers - pipe->nrbufs) << PAGE_SHIFT); + ret = do_splice_to(in, &pos, pipe, read_len, flags); if (unlikely(ret <= 0)) goto out_release;