Date:   Mon,  9 May 2022 20:00:12 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     mhocko@...e.com, rientjes@...gle.com, willy@...radead.org,
        hannes@...xchg.org, guro@...com, minchan@...nel.org,
        kirill@...temov.name, aarcange@...hat.com, brauner@...nel.org,
        hch@...radead.org, oleg@...hat.com, david@...hat.com,
        jannh@...gle.com, shakeelb@...gle.com, peterx@...hat.com,
        jhubbard@...dia.com, shuah@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, kernel-team@...roid.com,
        surenb@...gle.com
Subject: [PATCH 1/3] selftests: vm: add process_mrelease tests

Introduce process_mrelease syscall sanity tests. They include tests of
invalid pidfd and flags inputs, attempting to call process_mrelease
with a live process and a valid usage of process_mrelease. Because
process_mrelease has to be used against a process with a pending SIGKILL,
it's possible that the process exits before process_mrelease gets called.
In such cases we retry the test with a victim that allocates twice more
memory up to 1GB. This would require the victim process to spend more
time during exit and process_mrelease has a better chance of catching
the process before it exits.

Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
 tools/testing/selftests/vm/Makefile        |   1 +
 tools/testing/selftests/vm/mrelease_test.c | 176 +++++++++++++++++++++
 tools/testing/selftests/vm/run_vmtests.sh  |  16 ++
 3 files changed, 193 insertions(+)
 create mode 100644 tools/testing/selftests/vm/mrelease_test.c

diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
index 04a49e876a46..733fccbff0ef 100644
--- a/tools/testing/selftests/vm/Makefile
+++ b/tools/testing/selftests/vm/Makefile
@@ -43,6 +43,7 @@ TEST_GEN_FILES += map_populate
 TEST_GEN_FILES += memfd_secret
 TEST_GEN_FILES += mlock-random-test
 TEST_GEN_FILES += mlock2-tests
+TEST_GEN_FILES += mrelease_test
 TEST_GEN_FILES += mremap_dontunmap
 TEST_GEN_FILES += mremap_test
 TEST_GEN_FILES += on-fault-limit
diff --git a/tools/testing/selftests/vm/mrelease_test.c b/tools/testing/selftests/vm/mrelease_test.c
new file mode 100644
index 000000000000..a61061bf8433
--- /dev/null
+++ b/tools/testing/selftests/vm/mrelease_test.c
@@ -0,0 +1,176 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2022 Google LLC
+ */
+#define _GNU_SOURCE
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "util.h"
+
+static inline int pidfd_open(pid_t pid, unsigned int flags)
+{
+#ifdef __NR_pidfd_open
+	return syscall(__NR_pidfd_open, pid, flags);
+#else
+	errno = ENOSYS;
+	return -1;
+#endif
+}
+
+static inline int process_mrelease(int pidfd, unsigned int flags)
+{
+#ifdef __NR_process_mrelease
+	return syscall(__NR_process_mrelease, pidfd, flags);
+#else
+	errno = ENOSYS;
+	return -1;
+#endif
+}
+
+static void write_fault_pages(char *addr, unsigned long nr_pages)
+{
+	unsigned long i;
+
+	for (i = 0; i < nr_pages; i++)
+		*((unsigned long *)(addr + (i * PAGE_SIZE))) = i;
+}
+
+static int alloc_noexit(unsigned long nr_pages, int pipefd)
+{
+	int ppid = getppid();
+	void *buf;
+
+	buf = mmap(NULL, nr_pages * PAGE_SIZE, PROT_READ | PROT_WRITE,
+		   MAP_PRIVATE | MAP_ANON, 0, 0);
+	if (buf == MAP_FAILED) {
+		perror("mmap");
+		return 1;
+	}
+
+	write_fault_pages((char *)buf, nr_pages);
+
+	/* Signal the parent that the child is ready */
+	if (write(pipefd, "", 1) < 0) {
+		perror("write");
+		return 1;
+	}
+
+	/* Wait to be killed (when reparenting happens) */
+	while (getppid() == ppid)
+		sleep(1);
+
+	munmap(buf, nr_pages * PAGE_SIZE);
+
+	return 0;
+}
+
+
+#define MB(x) (x << 20)
+#define MAX_SIZE_MB 1024
+
+int main(void)
+{
+	int res;
+	int pipefd[2], pidfd;
+	pid_t pid;
+	char byte;
+	size_t size;
+	int negative_tests_done = 0;
+
+	/* Test a wrong pidfd */
+	if (!process_mrelease(-1, 0) || errno != EBADF) {
+		perror("process_mrelease with wring pidfd");
+		exit(1);
+	}
+
+	/*
+	 * Start the test with 1MB allocation and double every time
+	 * process_mrelease fails
+	 */
+	for (size = 1; size <= MAX_SIZE_MB; size *= 2) {
+		/*
+		 * Pipe for the child to signal when it's done allocating
+		 * memory
+		 */
+		if (pipe(pipefd)) {
+			perror("pipe");
+			exit(1);
+		}
+		pid = fork();
+		if (pid < 0) {
+			perror("fork");
+			exit(1);
+		}
+
+		if (pid == 0) {
+			close(pipefd[0]);
+			res = alloc_noexit(MB(size) / PAGE_SIZE, pipefd[1]);
+			close(pipefd[1]);
+			exit(res);
+		}
+
+		close(pipefd[1]);
+		/* Block until the child is ready */
+		res = read(pipefd[0], &byte, 1);
+		close(pipefd[0]);
+		if (res < 0) {
+			perror("read");
+			exit(1);
+		}
+
+		pidfd = pidfd_open(pid, 0);
+		if (pidfd < 0) {
+			perror("pidfd_open");
+			exit(1);
+		}
+
+		/* Run negative tests which require a valid child only once */
+		if (!negative_tests_done) {
+			/* Test invalid flags */
+			if (!process_mrelease(pidfd, (unsigned int)-1) ||
+			    errno != EINVAL) {
+				perror("process_mrelease with wrong flags");
+				exit(1);
+			}
+			/* Test reapling while process is still alive */
+			if (!process_mrelease(pidfd, 0) ||
+			    errno != EINVAL) {
+				perror("process_mrelease on a live process");
+				exit(1);
+			}
+			negative_tests_done = 1;
+		}
+
+		if (kill(pid, SIGKILL)) {
+			perror("kill");
+			exit(1);
+		}
+
+		if (!process_mrelease(pidfd, 0)) {
+			/* Terminate the test once process_mrelease succeeds */
+			return 0;
+		}
+
+		/*
+		 * Ignore the failure if the child exited before mrelease got
+		 * called, increase allocation size and retry the test
+		 */
+		if (errno != ESRCH) {
+			perror("process_mrelease");
+			exit(1);
+		}
+
+		if (waitpid(pid, NULL, 0) < 0) {
+			perror("waitpid");
+			exit(1);
+		}
+		close(pidfd);
+	}
+
+	printf("All process_mrelease attempts failed!\n");
+	exit(1);
+}
diff --git a/tools/testing/selftests/vm/run_vmtests.sh b/tools/testing/selftests/vm/run_vmtests.sh
index 352ba00cf26b..1986162fea39 100755
--- a/tools/testing/selftests/vm/run_vmtests.sh
+++ b/tools/testing/selftests/vm/run_vmtests.sh
@@ -287,6 +287,22 @@ else
 	echo "[PASS]"
 fi
 
+echo "---------------------"
+echo "running mrelease_test"
+echo "---------------------"
+./mrelease_test
+ret_val=$?
+
+if [ $ret_val -eq 0 ]; then
+	echo "[PASS]"
+elif [ $ret_val -eq $ksft_skip ]; then
+	 echo "[SKIP]"
+	 exitcode=$ksft_skip
+else
+	echo "[FAIL]"
+	exitcode=1
+fi
+
 echo "-------------------"
 echo "running mremap_test"
 echo "-------------------"
-- 
2.36.0.512.ge40c2bad7a-goog

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