From: Aboorva Devarajan <aboorvad@linux.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org
Cc: Jason Gunthorpe <jgg@ziepe.ca>, Leon Romanovsky <leon@kernel.org>,
David Hildenbrand <david@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>,
"Liam R . Howlett" <liam@infradead.org>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, Shuah Khan <shuah@kernel.org>,
Ralph Campbell <rcampbell@nvidia.com>,
Matthew Brost <matthew.brost@intel.com>,
Balbir Singh <balbirs@nvidia.com>,
Alistair Popple <apopple@nvidia.com>,
Alex Sierra <alex.sierra@amd.com>,
Matthew Wilcox <willy@infradead.org>,
Sayali Patil <sayalip@linux.ibm.com>,
linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
Aboorva Devarajan <aboorvad@linux.ibm.com>
Subject: [PATCH v3 3/3] selftests/mm: fix exclusive_cow test fork() handling
Date: Thu, 11 Jun 2026 09:11:02 +0530 [thread overview]
Message-ID: <20260611034102.1030738-4-aboorvad@linux.ibm.com> (raw)
In-Reply-To: <20260611034102.1030738-1-aboorvad@linux.ibm.com>
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 <aboorvad@linux.ibm.com>
---
tools/testing/selftests/mm/hmm-tests.c | 31 +++++++++++++++++++++++---
1 file changed, 28 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
index 8f4f82467043..e4c49699f3f7 100644
--- a/tools/testing/selftests/mm/hmm-tests.c
+++ b/tools/testing/selftests/mm/hmm-tests.c
@@ -1884,6 +1884,8 @@ 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);
@@ -1912,14 +1914,37 @@ 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 verifies COW independently, then _exit(0)s so it does
+ * not run the test teardown. A failed ASSERT_* here makes the
+ * harness abort() the child, so the parent sees
+ * !WIFEXITED(status) below and fails in turn.
+ */
+ 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
next prev parent reply other threads:[~2026-06-11 3:42 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-11 3:40 [PATCH v3 0/3] selftests/mm: assorted fixes for hmm-tests Aboorva Devarajan
2026-06-11 3:41 ` [PATCH v3 1/3] selftests/mm: allow PUD-level entries in compound testcase of hmm tests Aboorva Devarajan
2026-06-15 0:16 ` Balbir Singh
2026-06-24 3:34 ` Aboorva Devarajan
2026-06-11 3:41 ` [PATCH v3 2/3] selftests/mm: remove hardcoded THP sizing assumptions in " Aboorva Devarajan
2026-06-12 8:22 ` Balbir Singh
2026-06-11 3:41 ` Aboorva Devarajan [this message]
2026-06-11 4:59 ` [PATCH v3 3/3] selftests/mm: fix exclusive_cow test fork() handling Balbir Singh
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260611034102.1030738-4-aboorvad@linux.ibm.com \
--to=aboorvad@linux.ibm.com \
--cc=akpm@linux-foundation.org \
--cc=alex.sierra@amd.com \
--cc=apopple@nvidia.com \
--cc=balbirs@nvidia.com \
--cc=david@kernel.org \
--cc=jgg@ziepe.ca \
--cc=leon@kernel.org \
--cc=liam@infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=ljs@kernel.org \
--cc=matthew.brost@intel.com \
--cc=mhocko@suse.com \
--cc=rcampbell@nvidia.com \
--cc=rppt@kernel.org \
--cc=sayalip@linux.ibm.com \
--cc=shuah@kernel.org \
--cc=surenb@google.com \
--cc=vbabka@kernel.org \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.