From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Amir Goldstein <amir73il@gmail.com>, Dave Chinner <david@fromorbit.com>
Cc: jencce.kernel@gmail.com, linux-xfs <linux-xfs@vger.kernel.org>,
overlayfs <linux-unionfs@vger.kernel.org>,
Zorro Lang <zlang@redhat.com>, fstests <fstests@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Christoph Hellwig <hch@infradead.org>
Subject: [PATCH v2 1/2] splice: don't read more than available pipe space
Date: Sun, 2 Dec 2018 10:08:32 -0800 [thread overview]
Message-ID: <20181202180832.GR8125@magnolia> (raw)
From: Darrick J. Wong <darrick.wong@oracle.com>
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")
Reported-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
v2: split into two parts per hch request
---
fs/splice.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
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;
next reply other threads:[~2018-12-02 18:09 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-02 18:08 Darrick J. Wong [this message]
2018-12-02 18:10 ` [PATCH v2 2/2] iomap: partially revert 4721a601099 (simulated directio short read on EFAULT) Darrick J. Wong
2018-12-02 19:37 ` Amir Goldstein
2019-08-21 20:23 ` Andreas Grünbacher
2019-08-28 14:23 ` Darrick J. Wong
2019-08-28 14:37 ` Andreas Grünbacher
2019-08-29 3:12 ` Darrick J. Wong
2019-08-29 11:49 ` Andreas Grünbacher
2019-08-29 1:36 ` Zorro Lang
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