diff --git a/src/uu/tail/src/tail.rs b/src/uu/tail/src/tail.rs
index 899400c9589..f579c6a1128 100644
--- a/src/uu/tail/src/tail.rs
+++ b/src/uu/tail/src/tail.rs
@@ -596,7 +596,7 @@ fn print_target_section<
         }
     } else {
         #[cfg(any(target_os = "linux", target_os = "android"))]
-        if uucore::pipes::splice_unbounded_broker(file, &mut stdout)? {
+        if uucore::pipes::splice_unbounded_broker(file, &mut stdout)?.is_err() {
             io::copy(file, &mut stdout)?;
         }
         #[cfg(not(any(target_os = "linux", target_os = "android")))]
diff --git a/src/uucore/src/lib/features/buf_copy/linux.rs b/src/uucore/src/lib/features/buf_copy/linux.rs
index df1f33416f7..f8eaeb1d647 100644
--- a/src/uucore/src/lib/features/buf_copy/linux.rs
+++ b/src/uucore/src/lib/features/buf_copy/linux.rs
@@ -4,14 +4,7 @@
 // file that was distributed with this source code.
 
 //! Buffer-based copying implementation for Linux and Android.
-
-use crate::error::UResult;
-
-/// Buffer-based copying utilities for unix (excluding Linux).
-use std::{
-    io::{Read, Write},
-    os::fd::AsFd,
-};
+use std::os::fd::AsFd;
 
 /// Copy data from `Read` implementor `source` into a `Write` implementor
 /// `dest`. This works by reading a chunk of data from `source` and writing the
@@ -24,26 +17,16 @@ use std::{
 /// # Arguments
 /// * `source` - `Read` implementor to copy data from.
 /// * `dest` - `Write` implementor to copy data to.
-pub fn copy_stream<R, S>(src: &mut R, dest: &mut S) -> UResult<()>
-where
-    R: Read + AsFd,
-    S: Write + AsFd,
-{
+pub fn copy_stream(
+    src: &mut (impl std::io::Read + AsFd),
+    dest: &mut impl AsFd,
+) -> crate::error::UResult<()> {
     // If we're on Linux or Android, try to use the splice() system call
     // for faster writing. If it works, we're done.
-    // todo: bypass broker pipe this if input or output is pipe. We use this mostly for stream.
-    if !crate::pipes::splice_unbounded_broker(src, dest)? {
-        return Ok(());
+    if crate::pipes::splice_unbounded_auto(src, dest)? {
+        // If the splice() call failed, fall back on writing "without buffering", or order of output would be wrong
+        // unrelated for cp /dev/stdin since cp does not have multiple input? <https://github.com/uutils/coreutils/issues/5186>
+        std::io::copy(src, &mut crate::io::RawWriter(dest))?;
     }
-
-    // If the splice() call failed, fall back on slower writing.
-    std::io::copy(src, dest)?;
-
-    // If the splice() call failed and there has been some data written to
-    // stdout via while loop above AND there will be second splice() call
-    // that will succeed, data pushed through splice will be output before
-    // the data buffered in stdout.lock. Therefore additional explicit flush
-    // is required here.
-    dest.flush()?;
     Ok(())
 }
diff --git a/src/uucore/src/lib/features/pipes.rs b/src/uucore/src/lib/features/pipes.rs
index 2501a9d44a8..7b9310005b9 100644
--- a/src/uucore/src/lib/features/pipes.rs
+++ b/src/uucore/src/lib/features/pipes.rs
@@ -100,19 +100,24 @@ pub fn splice_unbounded(source: &impl AsFd, dest: &mut impl AsFd) -> rustix::io:
     Ok(())
 }
 
-/// force-splice source to dest even both of them are not pipe
-/// return true if we need read/write fallback
+/// force-splice source to dest even both of them are not pipe via broker pipe
+/// returns Ok(Ok(())) if splice succeeds
+/// returns Ok(Err()) if splice failed, but you can fallback to read/write
+/// returns std::io::Result if splice from broker failed and read/write fallback from broker failed
 ///
+/// Thus, ?.is_err() returns serious error at early stage and checks that you can fallback
 /// This should not be used if one of them are pipe to save resources
 #[inline]
 #[cfg(any(target_os = "linux", target_os = "android"))]
-pub fn splice_unbounded_broker(source: &impl AsFd, dest: &mut impl AsFd) -> std::io::Result<bool> {
+pub fn splice_unbounded_broker(
+    source: &impl AsFd,
+    dest: &mut impl AsFd,
+) -> std::io::Result<Result<(), ()>> {
     static PIPE_CACHE: OnceLock<Option<(PipeReader, PipeWriter)>> = OnceLock::new();
-    let Some((pipe_rd, pipe_wr)) = PIPE_CACHE
-        .get_or_init(|| pipe::<false>(MAX_ROOTLESS_PIPE_SIZE).ok())
-        .as_ref()
+    let Some((pipe_rd, pipe_wr)) =
+        PIPE_CACHE.get_or_init(|| pipe::<false>(MAX_ROOTLESS_PIPE_SIZE).ok())
     else {
-        return Ok(true);
+        return Ok(Err(()));
     };
     // improve throughput
     // no need to increase pipe size of input fd since
@@ -122,7 +127,7 @@ pub fn splice_unbounded_broker(source: &impl AsFd, dest: &mut impl AsFd) -> std:
 
     loop {
         match splice(&source, &pipe_wr, MAX_ROOTLESS_PIPE_SIZE) {
-            Ok(0) => return Ok(false),
+            Ok(0) => return Ok(Ok(())),
             Ok(n) => {
                 if splice_exact(&pipe_rd, dest, n).is_err() {
                     // If the first splice manages to copy to the intermediate
@@ -135,10 +140,10 @@ pub fn splice_unbounded_broker(source: &impl AsFd, dest: &mut impl AsFd) -> std:
                     let mut drain = Vec::with_capacity(n);
                     pipe_rd.take(n as u64).read_to_end(&mut drain)?;
                     RawWriter(&dest).write_all(&drain)?;
-                    return Ok(true);
+                    return Ok(Err(()));
                 }
             }
-            Err(_) => return Ok(true),
+            Err(_) => return Ok(Err(())),
         }
     }
 }
@@ -153,7 +158,7 @@ pub fn splice_unbounded_auto(source: &impl AsFd, dest: &mut impl AsFd) -> std::i
     // use splice to check that input or output is pipe which is efficient
     let fallback = match splice(&source, dest, MAX_ROOTLESS_PIPE_SIZE) {
         Ok(_) => splice_unbounded(source, dest).is_err(),
-        _ => splice_unbounded_broker(source, dest)?,
+        _ => splice_unbounded_broker(source, dest)?.is_err(),
     };
     Ok(fallback)
 }