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Message-ID: <915443.1755207950@warthog.procyon.org.uk>
Date: Thu, 14 Aug 2025 22:45:50 +0100
From: David Howells <dhowells@...hat.com>
To: Christian Brauner <brauner@...nel.org>,
Paulo Alcantara <pc@...guebit.org>, Steve French <sfrench@...ba.org>
cc: dhowells@...hat.com, Xiaoli Feng <fengxiaoli0714@...il.com>,
Shyam Prasad N <sprasad@...rosoft.com>, netfs@...ts.linux.dev,
linux-cifs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] netfs: Fix unbuffered write error handling
If all the subrequests in an unbuffered write stream fail, the subrequest
collector doesn't update the stream->transferred value and it retains its
initial LONG_MAX value. Unfortunately, if all active streams fail, then we
take the smallest value of { LONG_MAX, LONG_MAX, ... } as the value to set
in wreq->transferred - which is then returned from ->write_iter().
LONG_MAX was chosen as the initial value so that all the streams can be
quickly assessed by taking the smallest value of all stream->transferred -
but this only works if we've set any of them.
Fix this by adding a flag to indicate whether the value in
stream->transferred is valid and checking that when we integrate the
values. stream->transferred can then be initialised to zero.
This was found by running the generic/750 xfstest against cifs with
cache=none. It splices data to the target file. Once (if) it has used up
all the available scratch space, the writes start failing with ENOSPC.
This causes ->write_iter() to fail. However, it was returning
wreq->transferred, i.e. LONG_MAX, rather than an error (because it thought
the amount transferred was non-zero) and iter_file_splice_write() would
then try to clean up that amount of pipe bufferage - leading to an oops
when it overran. The kernel log showed:
CIFS: VFS: Send error in write = -28
followed by:
BUG: kernel NULL pointer dereference, address: 0000000000000008
with:
RIP: 0010:iter_file_splice_write+0x3a4/0x520
do_splice+0x197/0x4e0
or:
RIP: 0010:pipe_buf_release (include/linux/pipe_fs_i.h:282)
iter_file_splice_write (fs/splice.c:755)
Also put a warning check into splice to announce if ->write_iter() returned
that it had written more than it was asked to.
Fixes: 288ace2f57c9 ("netfs: New writeback implementation")
Reported-by: Xiaoli Feng <fengxiaoli0714@...il.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220445
Signed-off-by: David Howells <dhowells@...hat.com>
cc: Paulo Alcantara <pc@...guebit.org>
cc: Steve French <sfrench@...ba.org>
cc: Shyam Prasad N <sprasad@...rosoft.com>
cc: netfs@...ts.linux.dev
cc: linux-cifs@...r.kernel.org
cc: linux-fsdevel@...r.kernel.org
cc: stable@...r.kernel.org
---
fs/netfs/read_collect.c | 4 +++-
fs/netfs/write_collect.c | 10 ++++++++--
fs/netfs/write_issue.c | 4 ++--
fs/splice.c | 3 +++
include/linux/netfs.h | 1 +
5 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
index 3e804da1e1eb..a95e7aadafd0 100644
--- a/fs/netfs/read_collect.c
+++ b/fs/netfs/read_collect.c
@@ -281,8 +281,10 @@ static void netfs_collect_read_results(struct netfs_io_request *rreq)
} else if (test_bit(NETFS_RREQ_SHORT_TRANSFER, &rreq->flags)) {
notes |= MADE_PROGRESS;
} else {
- if (!stream->failed)
+ if (!stream->failed) {
stream->transferred += transferred;
+ stream->transferred_valid = true;
+ }
if (front->transferred < front->len)
set_bit(NETFS_RREQ_SHORT_TRANSFER, &rreq->flags);
notes |= MADE_PROGRESS;
diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index 0f3a36852a4d..cbf3d9194c7b 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -254,6 +254,7 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
if (front->start + front->transferred > stream->collected_to) {
stream->collected_to = front->start + front->transferred;
stream->transferred = stream->collected_to - wreq->start;
+ stream->transferred_valid = true;
notes |= MADE_PROGRESS;
}
if (test_bit(NETFS_SREQ_FAILED, &front->flags)) {
@@ -356,6 +357,7 @@ bool netfs_write_collection(struct netfs_io_request *wreq)
{
struct netfs_inode *ictx = netfs_inode(wreq->inode);
size_t transferred;
+ bool transferred_valid = false;
int s;
_enter("R=%x", wreq->debug_id);
@@ -376,12 +378,16 @@ bool netfs_write_collection(struct netfs_io_request *wreq)
continue;
if (!list_empty(&stream->subrequests))
return false;
- if (stream->transferred < transferred)
+ if (stream->transferred_valid &&
+ stream->transferred < transferred) {
transferred = stream->transferred;
+ transferred_valid = true;
+ }
}
/* Okay, declare that all I/O is complete. */
- wreq->transferred = transferred;
+ if (transferred_valid)
+ wreq->transferred = transferred;
trace_netfs_rreq(wreq, netfs_rreq_trace_write_done);
if (wreq->io_streams[1].active &&
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 50bee2c4130d..0584cba1a043 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -118,12 +118,12 @@ struct netfs_io_request *netfs_create_write_req(struct address_space *mapping,
wreq->io_streams[0].prepare_write = ictx->ops->prepare_write;
wreq->io_streams[0].issue_write = ictx->ops->issue_write;
wreq->io_streams[0].collected_to = start;
- wreq->io_streams[0].transferred = LONG_MAX;
+ wreq->io_streams[0].transferred = 0;
wreq->io_streams[1].stream_nr = 1;
wreq->io_streams[1].source = NETFS_WRITE_TO_CACHE;
wreq->io_streams[1].collected_to = start;
- wreq->io_streams[1].transferred = LONG_MAX;
+ wreq->io_streams[1].transferred = 0;
if (fscache_resources_valid(&wreq->cache_resources)) {
wreq->io_streams[1].avail = true;
wreq->io_streams[1].active = true;
diff --git a/fs/splice.c b/fs/splice.c
index 4d6df083e0c0..f5094b6d00a0 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -739,6 +739,9 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
sd.pos = kiocb.ki_pos;
if (ret <= 0)
break;
+ WARN_ONCE(ret > sd.total_len - left,
+ "Splice Exceeded! ret=%zd tot=%zu left=%zu\n",
+ ret, sd.total_len, left);
sd.num_spliced += ret;
sd.total_len -= ret;
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 185bd8196503..98c96d649bf9 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -150,6 +150,7 @@ struct netfs_io_stream {
bool active; /* T if stream is active */
bool need_retry; /* T if this stream needs retrying */
bool failed; /* T if this stream failed */
+ bool transferred_valid; /* T is ->transferred is valid */
};
/*
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