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Mon, 4 May 2026 09:11:15 +0000 (GMT) From: Aboorva Devarajan To: Andrew Morton , Shuah Khan , linux-mm@kvack.org, linux-kselftest@vger.kernel.org Cc: Sayali Patil , linux-kernel@vger.kernel.org, Aboorva Devarajan Subject: [PATCH 3/3] selftests/mm: fix exclusive_cow test fork() handling Date: Mon, 4 May 2026 14:41:08 +0530 Message-ID: X-Mailer: git-send-email 2.54.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: CLrEPZepVvPWW--8jC581KAg740SAxfb X-Proofpoint-GUID: CLrEPZepVvPWW--8jC581KAg740SAxfb X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTA0MDA5NyBTYWx0ZWRfX7828XjCc7lDp W8qiv4I7CvqzBOmj/pcjx0dkovueJ/A9+xgYOCoCwlsC+YoB4oKjwjrKNNrHTiYcJEm0BUUsjlh pkIaOOhPEy+t/n8kABgOC3+DftyLjCiwpNUC11c1fJ5CucRN7wUj4X+m4c4CEHlgFbl0hPMEIWg dTWx1GZ30G1ZUS+IqWR/96+6imawGwcF32NujWVlWOMht7C/eq5jdJydaOGRsMsef9qreffaGya /2fKwqcZZiwQzoE4jJCIKRTPWfHRRCHJQF9Puwx/AbL4GtjP0HvwFHMUKZwgkkFPDxjntAHvn87 WewUU7C1VN+0NGzl2bZOx4Xia3xIqpho7ptYiZGT5KAOB4yM0w80K+qIQOKhlFsawAxE335+JiW XCbTn0h8TOFffsQyM1ACwTuD3qwKLJwakCwuyqS1m+X3zh10v77+aRmHkn4UVIOADN7yIi+OGB9 Q+sHi9QHCXs5amEwBXQ== X-Authority-Analysis: v=2.4 cv=UbFhjqSN c=1 sm=1 tr=0 ts=69f862b9 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=YKbGnN07TdQTFoDUIKcA:9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-04_03,2026-04-30_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 spamscore=0 lowpriorityscore=0 malwarescore=0 suspectscore=0 adultscore=0 priorityscore=1501 bulkscore=0 phishscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605040097 The test ignores the return value of fork(), so both the parent and the (newly created) child run the COW verification loops and then call hmm_buffer_free() before returning into the kselftest harness, which _exit()s each side. This duplicated teardown sequence has been observed to manifest as a SIGSEGV in the test child, e.g.: hmm-tests[360141]: segfault (11) at 0 nip 10006964 lr 1000ac3c code 1 in hmm-tests[6964,10000000+30000] Fix this by adopting the same fork()-then-wait pattern already used by the nearby anon_write_child / anon_write_child_shared tests in this file: the child performs the COW verification and then _exit(0)s so it does not run the test teardown, while the parent independently verifies COW, waits for the child, and only then frees the buffer. Fixes: b659baea75469 ("mm: selftests for exclusive device memory") Signed-off-by: Aboorva Devarajan --- tools/testing/selftests/mm/hmm-tests.c | 30 +++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-) diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c index 1e5c1432ef6b..c5000d53b604 100644 --- a/tools/testing/selftests/mm/hmm-tests.c +++ b/tools/testing/selftests/mm/hmm-tests.c @@ -1866,6 +1866,8 @@ TEST_F(hmm, exclusive_cow) unsigned long i; int *ptr; int ret; + pid_t pid; + int status; npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift; ASSERT_NE(npages, 0); @@ -1894,14 +1896,36 @@ TEST_F(hmm, exclusive_cow) ASSERT_EQ(ret, 0); ASSERT_EQ(buffer->cpages, npages); - fork(); + pid = fork(); + if (pid == -1) + ASSERT_EQ(pid, 0); - /* Fault pages back to system memory and check them. */ + if (pid == 0) { + /* + * Child: fault pages back and verify COW, then _exit(). + * On ASSERT failure the harness calls abort(); the parent + * reports it via the WIFEXITED/WEXITSTATUS checks below. + */ + for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i) + ASSERT_EQ(ptr[i]++, i); + + for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i) + ASSERT_EQ(ptr[i], i + 1); + + _exit(0); + } + + /* Parent: also increment to verify COW works for both processes. */ for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i) ASSERT_EQ(ptr[i]++, i); for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i) - ASSERT_EQ(ptr[i], i+1); + ASSERT_EQ(ptr[i], i + 1); + + /* Parent: wait for child and then free the buffer. */ + ASSERT_EQ(waitpid(pid, &status, 0), pid); + ASSERT_TRUE(WIFEXITED(status)); + ASSERT_EQ(WEXITSTATUS(status), 0); hmm_buffer_free(buffer); } -- 2.54.0