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Date:   Thu,  6 Jul 2023 15:50:35 -0700
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Subject: [PATCH v3 7/8] selftests/mm: refactor uffd_poll_thread to allow
 custom fault handlers
From:   Axel Rasmussen <axelrasmussen@google.com>
To:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Brian Geffon <bgeffon@google.com>,
        Christian Brauner <brauner@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Gaosheng Cui <cuigaosheng1@huawei.com>,
        Huang Ying <ying.huang@intel.com>,
        Hugh Dickins <hughd@google.com>,
        James Houghton <jthoughton@google.com>,
        "Jan Alexander Steffens (heftig)" <heftig@archlinux.org>,
        Jiaqi Yan <jiaqiyan@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        "Liam R. Howlett" <Liam.Howlett@oracle.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        "Mike Rapoport (IBM)" <rppt@kernel.org>,
        Muchun Song <muchun.song@linux.dev>,
        Nadav Amit <namit@vmware.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Peter Xu <peterx@redhat.com>,
        Ryan Roberts <ryan.roberts@arm.com>,
        Shuah Khan <shuah@kernel.org>,
        Suleiman Souhlal <suleiman@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        "T.J. Alumbaugh" <talumbau@google.com>,
        Yu Zhao <yuzhao@google.com>,
        ZhangPeng <zhangpeng362@huawei.com>
Cc:     linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kselftest@vger.kernel.org,
        Axel Rasmussen <axelrasmussen@google.com>
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Precedence: bulk

Previously, we had "one fault handler to rule them all", which used
several branches to deal with all of the scenarios required by all of
the various tests.

In upcoming patches, I plan to add a new test, which has its own
slightly different fault handling logic. Instead of continuing to add
cruft to the existing fault handler, let's allow tests to define custom
ones, separate from other tests.

Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
---
 tools/testing/selftests/mm/uffd-common.c |  5 ++++-
 tools/testing/selftests/mm/uffd-common.h |  3 +++
 tools/testing/selftests/mm/uffd-stress.c | 12 +++++++-----
 3 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c
index ba20d7504022..02b89860e193 100644
--- a/tools/testing/selftests/mm/uffd-common.c
+++ b/tools/testing/selftests/mm/uffd-common.c
@@ -499,6 +499,9 @@ void *uffd_poll_thread(void *arg)
 	int ret;
 	char tmp_chr;
 
+	if (!args->handle_fault)
+		args->handle_fault = uffd_handle_page_fault;
+
 	pollfd[0].fd = uffd;
 	pollfd[0].events = POLLIN;
 	pollfd[1].fd = pipefd[cpu*2];
@@ -527,7 +530,7 @@ void *uffd_poll_thread(void *arg)
 			err("unexpected msg event %u\n", msg.event);
 			break;
 		case UFFD_EVENT_PAGEFAULT:
-			uffd_handle_page_fault(&msg, args);
+			args->handle_fault(&msg, args);
 			break;
 		case UFFD_EVENT_FORK:
 			close(uffd);
diff --git a/tools/testing/selftests/mm/uffd-common.h b/tools/testing/selftests/mm/uffd-common.h
index 197f5262fe0d..7c4fa964c3b0 100644
--- a/tools/testing/selftests/mm/uffd-common.h
+++ b/tools/testing/selftests/mm/uffd-common.h
@@ -77,6 +77,9 @@ struct uffd_args {
 	unsigned long missing_faults;
 	unsigned long wp_faults;
 	unsigned long minor_faults;
+
+	/* A custom fault handler; defaults to uffd_handle_page_fault. */
+	void (*handle_fault)(struct uffd_msg *msg, struct uffd_args *args);
 };
 
 struct uffd_test_ops {
diff --git a/tools/testing/selftests/mm/uffd-stress.c b/tools/testing/selftests/mm/uffd-stress.c
index 995ff13e74c7..50b1224d72c7 100644
--- a/tools/testing/selftests/mm/uffd-stress.c
+++ b/tools/testing/selftests/mm/uffd-stress.c
@@ -189,10 +189,8 @@ static int stress(struct uffd_args *args)
 				   locking_thread, (void *)cpu))
 			return 1;
 		if (bounces & BOUNCE_POLL) {
-			if (pthread_create(&uffd_threads[cpu], &attr,
-					   uffd_poll_thread,
-					   (void *)&args[cpu]))
-				return 1;
+			if (pthread_create(&uffd_threads[cpu], &attr, uffd_poll_thread, &args[cpu]))
+				err("uffd_poll_thread create");
 		} else {
 			if (pthread_create(&uffd_threads[cpu], &attr,
 					   uffd_read_thread,
@@ -247,9 +245,13 @@ static int userfaultfd_stress(void)
 {
 	void *area;
 	unsigned long nr;
-	struct uffd_args args[nr_cpus];
+	struct uffd_args *args;
 	uint64_t mem_size = nr_pages * page_size;
 
+	args = calloc(nr_cpus, sizeof(struct uffd_args));
+	if (!args)
+		err("allocating args array failed");
+
 	if (uffd_test_ctx_init(UFFD_FEATURE_WP_UNPOPULATED, NULL))
 		err("context init failed");
 
-- 
2.41.0.255.g8b1d071c50-goog