splice() from pipe should return 0 when there is no pipe writer. However,
since commit a194dfe6e6f6f720 ("pipe: Rearrange sequence in pipe_write()
to preallocate slot") started inserting empty pages, splice() from pipe
also returns 0 when all ready buffers are empty pages.
----------
#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
const int fd = open("/tmp/testfile", O_WRONLY | O_CREAT, 0600);
int pipe_fd[2] = { -1, -1 };
pipe(pipe_fd);
write(pipe_fd[1], NULL, 4096);
/* This splice() should wait unless interrupted. */
return !splice(pipe_fd[0], NULL, fd, NULL, 65536, 0);
}
----------
Since such behavior might confuse splice() users, let's fix it by waiting
for non-empty pages inside splice_from_pipe_next().
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Fixes: a194dfe6e6f6f720 ("pipe: Rearrange sequence in pipe_write() to preallocate slot")
Cc: stable@xxxxxxxxxxxxxxx # 5.5+
---
fs/splice.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/fs/splice.c b/fs/splice.c
index c3d00dfc7344..b58c7ebf6805 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -538,6 +538,8 @@ static int splice_from_pipe_feed(struct pipe_inode_info *pipe, struct splice_des
*/
static int splice_from_pipe_next(struct pipe_inode_info *pipe, struct splice_desc *sd)
{
+ unsigned int head, tail, mask;
+
/*
* Check for signal early to make process killable when there are
* always buffers available
@@ -545,6 +547,7 @@ static int splice_from_pipe_next(struct pipe_inode_info *pipe, struct splice_des
if (signal_pending(current))
return -ERESTARTSYS;
+ refill:
while (pipe_empty(pipe->head, pipe->tail)) {
if (!pipe->writers)
return 0;
@@ -566,7 +569,21 @@ static int splice_from_pipe_next(struct pipe_inode_info *pipe, struct splice_des
pipe_wait_readable(pipe);
}
- return 1;
+ head = pipe->head;
+ tail = pipe->tail;
+ mask = pipe->ring_size - 1;
+
+ /* dismiss the empty buffers */
+ while (!pipe_empty(head, tail)) {
+ struct pipe_buffer *buf = &pipe->bufs[tail & mask];
+
+ if (likely(buf->len))
+ return 1;
+ pipe_buf_release(pipe, buf);
+ pipe->tail = ++tail;
+ }
+ /* wait again if all buffers were empty */
+ goto refill;
}
/**
--
2.18.4
