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Mon, 04 May 2026 01:17:00 -0700 (PDT) Received: from vini ([2401:4900:8fcb:edbd:7155:edb6:dac:107e]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8352bfe7a49sm7644356b3a.46.2026.05.04.01.16.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 May 2026 01:17:00 -0700 (PDT) From: Vineet Agarwal To: shuah@kernel.org, akpm@linux-foundation.org Cc: linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, david@kernel.org, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, Vineet Agarwal Subject: [PATCH v4] selftests/mm: ksm-functional-tests: fix partial write handling Date: Mon, 4 May 2026 13:43:13 +0530 Message-ID: <20260504081638.683223-1-agarwal.vineet2006@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Update write() checks to properly detect and handle partial writes. Previously, the write() calls used <=3D 0 to detect failure. This condition is never true for partial writes (ret > 0 but ret < len), so partial writes were silently treated as success. Fix this by verifying that write() returns the full expected length and treating any mismatch as failure. Signed-off-by: Vineet Agarwal Changes in v4: - Simplify write() checks as suggested by Mike Rapoport - Remove temporary variables and use direct comparisons - Use a single len variable Acked-by: David Hildenbrand (Arm) Acked-by: Mike Rapoport (Microsoft) --- .../selftests/mm/ksm_functional_tests.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/test= ing/selftests/mm/ksm_functional_tests.c index 8d874c4754f3..31c06c72203f 100644 --- a/tools/testing/selftests/mm/ksm_functional_tests.c +++ b/tools/testing/selftests/mm/ksm_functional_tests.c @@ -498,6 +498,7 @@ static void test_prctl_fork(void) static int start_ksmd_and_set_frequency(char *pages_to_scan, char *sleep_m= s) { int ksm_fd; + size_t len; =20 ksm_fd =3D open("/sys/kernel/mm/ksm/run", O_RDWR); if (ksm_fd < 0) @@ -506,11 +507,13 @@ static int start_ksmd_and_set_frequency(char *pages_t= o_scan, char *sleep_ms) if (write(ksm_fd, "1", 1) !=3D 1) return -errno; =20 - if (write(pages_to_scan_fd, pages_to_scan, strlen(pages_to_scan)) <=3D 0) - return -errno; + len =3D strlen(pages_to_scan); + if (write(pages_to_scan_fd, pages_to_scan, len) !=3D len) + return -1; =20 - if (write(sleep_millisecs_fd, sleep_ms, strlen(sleep_ms)) <=3D 0) - return -errno; + len =3D strlen(sleep_ms); + if (write(sleep_millisecs_fd, sleep_ms, len) !=3D len) + return -1; =20 return 0; } @@ -526,11 +529,11 @@ static int stop_ksmd_and_restore_frequency(void) if (write(ksm_fd, "2", 1) !=3D 1) return -errno; =20 - if (write(pages_to_scan_fd, "100", 3) <=3D 0) - return -errno; + if (write(pages_to_scan_fd, "100", 3) !=3D 3) + return -1; =20 - if (write(sleep_millisecs_fd, "20", 2) <=3D 0) - return -errno; + if (write(sleep_millisecs_fd, "20", 2) !=3D 2) + return -1; =20 return 0; } --=20 2.54.0