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Sun, 03 May 2026 03:12:48 -0700 (PDT) Received: from vini ([2401:4900:8fcb:edbd:7155:edb6:dac:107e]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-364ebec736dsm7810834a91.3.2026.05.03.03.12.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 03 May 2026 03:12:47 -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 v3] selftests/mm: ksm-functional-tests: fix partial write handling Date: Sun, 3 May 2026 15:38:40 +0530 Message-ID: <20260503101229.654763-1-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: 8bit Update write() checks to properly detect and handle partial writes. Previously, partial writes (ret > 0 && ret != len) could be treated as success because write() does not set errno in this case and the code returned -errno. This could result in returning 0 and incorrectly signaling 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 v3: - Simplify error handling as suggested by reviewer - Return -1 when write() does not complete fully - Rebase patch against base tree --- .../selftests/mm/ksm_functional_tests.c | 27 +++++++++++++------ 1 file changed, 19 insertions(+), 8 deletions(-) diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c index 8d874c4754f3..4abd98be3f59 100644 --- a/tools/testing/selftests/mm/ksm_functional_tests.c +++ b/tools/testing/selftests/mm/ksm_functional_tests.c @@ -498,6 +498,8 @@ static void test_prctl_fork(void) static int start_ksmd_and_set_frequency(char *pages_to_scan, char *sleep_ms) { int ksm_fd; + ssize_t ret; + size_t len, sleep_len; ksm_fd = open("/sys/kernel/mm/ksm/run", O_RDWR); if (ksm_fd < 0) @@ -506,11 +508,17 @@ static int start_ksmd_and_set_frequency(char *pages_to_scan, char *sleep_ms) if (write(ksm_fd, "1", 1) != 1) return -errno; - if (write(pages_to_scan_fd, pages_to_scan, strlen(pages_to_scan)) <= 0) - return -errno; + len = strlen(pages_to_scan); - if (write(sleep_millisecs_fd, sleep_ms, strlen(sleep_ms)) <= 0) - return -errno; + ret = write(pages_to_scan_fd, pages_to_scan, len); + if (ret != len) + return -1; + + sleep_len = strlen(sleep_ms); + + ret = write(sleep_millisecs_fd, sleep_ms, sleep_len); + if (ret != sleep_len) + return -1; return 0; } @@ -518,6 +526,7 @@ static int start_ksmd_and_set_frequency(char *pages_to_scan, char *sleep_ms) static int stop_ksmd_and_restore_frequency(void) { int ksm_fd; + ssize_t ret; ksm_fd = open("/sys/kernel/mm/ksm/run", O_RDWR); if (ksm_fd < 0) @@ -526,11 +535,13 @@ static int stop_ksmd_and_restore_frequency(void) if (write(ksm_fd, "2", 1) != 1) return -errno; - if (write(pages_to_scan_fd, "100", 3) <= 0) - return -errno; + ret = write(pages_to_scan_fd, "100", 3); + if (ret != 3) + return -1; - if (write(sleep_millisecs_fd, "20", 2) <= 0) - return -errno; + ret = write(sleep_millisecs_fd, "20", 2); + if (ret != 2) + return -1; return 0; } -- 2.54.0