[PATCH 2/2] splice: add some pipe_buf_assert_len() checks

Oleg Nesterov
2025-02-09T15:08:50Z

After the previous patch the readers can't (hopefully) hit a zero-sized
buffer, add a few pipe_buf_assert_len() debugging checks.

pipe_buf_assert_len() can probably have more users, including the writers
which update pipe->head.

While at it, simplify eat_empty_buffer(), it can use pipe_buf(pipe->tail).

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
fs/splice.c | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 28cfa63aa236..fb7841c07edd 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -453,7 +453,7 @@ static int splice_from_pipe_feed(struct pipe_inode_info *pipe, struct splice_des
while (!pipe_empty(head, tail)) {
struct pipe_buffer *buf = &pipe->bufs[tail & mask];

- sd->len = buf->len;
+ sd->len = pipe_buf_assert_len(buf);
if (sd->len > sd->total_len)
sd->len = sd->total_len;

@@ -494,13 +494,11 @@ static int splice_from_pipe_feed(struct pipe_inode_info *pipe, struct splice_des
/* We know we have a pipe buffer, but maybe it's empty? */
static inline bool eat_empty_buffer(struct pipe_inode_info *pipe)
{
- unsigned int tail = pipe->tail;
- unsigned int mask = pipe->ring_size - 1;
- struct pipe_buffer *buf = &pipe->bufs[tail & mask];
+ struct pipe_buffer *buf = pipe_buf(pipe, pipe->tail);

- if (unlikely(!buf->len)) {
+ if (unlikely(!pipe_buf_assert_len(buf))) {
pipe_buf_release(pipe, buf);
- pipe->tail = tail+1;
+ pipe->tail++;
return true;
}

@@ -717,7 +715,7 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
left = sd.total_len;
for (n = 0; !pipe_empty(head, tail) && left && n < nbufs; tail++) {
struct pipe_buffer *buf = &pipe->bufs[tail & mask];
- size_t this_len = buf->len;
+ size_t this_len = pipe_buf_assert_len(buf);

/* zero-length bvecs are not supported, skip them */
if (!this_len)
@@ -852,7 +850,7 @@ ssize_t splice_to_socket(struct pipe_inode_info *pipe, struct file *out,
struct pipe_buffer *buf = &pipe->bufs[tail & mask];
size_t seg;

- if (!buf->len) {
+ if (!pipe_buf_assert_len(buf)) {
tail++;
continue;
}
--
2.25.1.362.g51ebf55