[LTP] [PATCH] splice08: Keep calling splice() until all bytes are spliced

[LTP] [PATCH] splice08: Keep calling splice() until all bytes are spliced

[Wake Liu via ltp]

splice() may transfer fewer bytes than requested, but the test fails
as soon as a single call does not splice the whole buffer.

/dev/zero and /dev/full use copy_splice_read(), which limits the
transfer to the number of pages it gets from alloc_pages_bulk(). Since
kernel commit 187ad460b841 ("mm/page_alloc: avoid page allocator
recursion with pagesets.lock held"), the bulk allocator allocates only
one page per call when page_owner is enabled. On kernels booted with
page_owner=on, every request larger than a page is therefore cut to
PAGE_SIZE bytes and the test fails:

  TPASS: splice(...) returned 4096
  TFAIL: Only part 4096 bytes of 5045 were spliced

A short count is valid splice() behavior, not a kernel bug, so keep
calling splice() until the whole buffer is in the pipe and fail only
if it stops making progress before that.

Signed-off-by: Wake Liu <wakel@google.com>
---
 testcases/kernel/syscalls/splice/splice08.c | 27 ++++++++++++++-------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/testcases/kernel/syscalls/splice/splice08.c b/testcases/kernel/syscalls/splice/splice08.c
index bd635ee7e..2af1c88b6 100644
--- a/testcases/kernel/syscalls/splice/splice08.c
+++ b/testcases/kernel/syscalls/splice/splice08.c
@@ -23,21 +23,30 @@ static void test_splice(unsigned int bytes, int dev_fd)
 {
 	int pipefd[2];
 	char buf[bytes];
-	size_t i;
+	size_t i, spliced = 0;
 	int fail = 0;
 
 	memset(buf, 0xff, sizeof(buf));
 
 	SAFE_PIPE(pipefd);
 
-	TST_EXP_POSITIVE(splice(dev_fd, NULL, pipefd[1], NULL, sizeof(buf), 0));
-
-	if (!TST_PASS)
-		goto ret;
-
-	if ((size_t)TST_RET != sizeof(buf)) {
-		tst_res(TFAIL, "Only part %lu bytes of %u were spliced",
-			TST_RET, bytes);
+	/*
+	 * splice() may transfer less than requested, e.g. with page_owner=on
+	 * copy_splice_read() gets only a single page per call, so keep
+	 * splicing until all bytes are in the pipe.
+	 */
+	do {
+		TST_EXP_POSITIVE(splice(dev_fd, NULL, pipefd[1], NULL,
+					sizeof(buf) - spliced, 0));
+		if (!TST_PASS)
+			goto ret;
+
+		spliced += TST_RET;
+	} while (TST_RET && spliced < sizeof(buf));
+
+	if (spliced != sizeof(buf)) {
+		tst_res(TFAIL, "Only part %zu bytes of %u were spliced",
+			spliced, bytes);
 		goto ret;
 	}
 
-- 
2.56.0.307.g5fe7bd680c-goog


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Re: [LTP] splice08: Keep calling splice() until all bytes are spliced

[linuxtestproject.agent]

Hi Wake,

On Fri Oct 30 03:13:28 2026 +0000, Wake Liu <wakel@google.com> wrote:
> splice08: Keep calling splice() until all bytes are spliced

Verdict - Reviewed

---
Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

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