The patch titled
Subject: memfd: add test for COW on MAP_PRIVATE and F_SEAL_FUTURE_WRITE mappings
has been added to the -mm tree. Its filename is
memfd-add-test-for-cow-on-map_private-and-f_seal_future_write-mappings.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/memfd-add-test-for-cow-on-map_private-and-f_seal_future_write-mappings.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/memfd-add-test-for-cow-on-map_private-and-f_seal_future_write-mappings.patch
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------------------------------------------------------
From: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>
Subject: memfd: add test for COW on MAP_PRIVATE and F_SEAL_FUTURE_WRITE mappings
In this test, the parent and child both have writable private mappings.
The test shows that without the patch in this series, the parent and child
shared the same memory which is incorrect. In other words, COW needs to
be triggered so any writes to child's copy stays local to the child.
Link: http://lkml.kernel.org/r/20191107195355.80608-2-joel@xxxxxxxxxxxxxxxxx
Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Nicolas Geoffray <ngeoffray@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
tools/testing/selftests/memfd/memfd_test.c | 36 +++++++++++++++++++
1 file changed, 36 insertions(+)
--- a/tools/testing/selftests/memfd/memfd_test.c~memfd-add-test-for-cow-on-map_private-and-f_seal_future_write-mappings
+++ a/tools/testing/selftests/memfd/memfd_test.c
@@ -290,6 +290,40 @@ static void mfd_assert_read_shared(int f
munmap(p, mfd_def_size);
}
+static void mfd_assert_fork_private_write(int fd)
+{
+ int *p;
+ pid_t pid;
+
+ p = mmap(NULL,
+ mfd_def_size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE,
+ fd,
+ 0);
+ if (p == MAP_FAILED) {
+ printf("mmap() failed: %m\n");
+ abort();
+ }
+
+ p[0] = 22;
+
+ pid = fork();
+ if (pid == 0) {
+ p[0] = 33;
+ exit(0);
+ } else {
+ waitpid(pid, NULL, 0);
+
+ if (p[0] != 22) {
+ printf("MAP_PRIVATE copy-on-write failed: %m\n");
+ abort();
+ }
+ }
+
+ munmap(p, mfd_def_size);
+}
+
static void mfd_assert_write(int fd)
{
ssize_t l;
@@ -760,6 +794,8 @@ static void test_seal_future_write(void)
mfd_assert_read_shared(fd2);
mfd_fail_write(fd2);
+ mfd_assert_fork_private_write(fd);
+
munmap(p, mfd_def_size);
close(fd2);
close(fd);
_
Patches currently in -mm which might be from joel@xxxxxxxxxxxxxxxxx are
mm-emit-tracepoint-when-rss-changes.patch
rss_stat-add-support-to-detect-rss-updates-of-external-mm.patch
memfd-add-test-for-cow-on-map_private-and-f_seal_future_write-mappings.patch
