[PULL 03/11] tests/tcg/multiarch/linux/linux-test: Don't try to test atime update

["Alex Bennée" <alex.bennee@linaro.org>]

From: Peter Maydell <peter.maydell@linaro.org>

The linux-test test includes an attempt to check the utime and stat
syscalls by setting the atime and mtime of a file to specific values,
and then calling stat() to check that the values read back correctly.

Unfortunately this is flaky, as it will fail if some other process
(for instance a virus scanner, backup program, etc) gets in and reads
the file between the utime() and stat() call, resulting in a host
syscall sequence like this:

utimensat(AT_FDCWD, "file2",
  [{tv_sec=1001, tv_nsec=0} /* 1970-01-01T01:16:41+0100 */,
   {tv_sec=1000, tv_nsec=0} /* 1970-01-01T01:16:40+0100 */], 0) = 0
# successfully set atime to 1001 and mtime to 1000
statx(AT_FDCWD, "file2", AT_STATX_SYNC_AS_STAT|AT_NO_AUTOMOUNT,
  STATX_BASIC_STATS,
  {stx_mask=STATX_BASIC_STATS|STATX_MNT_ID,
   stx_blksize=4096, stx_attributes=0, stx_nlink=1, stx_uid=32808,
   stx_gid=32808, stx_mode=S_IFREG|0600, stx_ino=21659016,
   stx_size=100, stx_blocks=8,
   stx_attributes_mask=STATX_ATTR_COMPRESSED|STATX_ATTR_IMMUTABLE|
         STATX_ATTR_APPEND|STATX_ATTR_NODUMP|STATX_ATTR_ENCRYPTED|
         STATX_ATTR_AUTOMOUNT|STATX_ATTR_MOUNT_ROOT|STATX_ATTR_VERITY|
         STATX_ATTR_DAX,
   stx_atime={tv_sec=1760091862, tv_nsec=63509009} /* 2025-10-10T11:24:22.063509009+0100 */,
   stx_ctime={tv_sec=1760091862, tv_nsec=63509009} /* 2025-10-10T11:24:22.063509009+0100 */,
   stx_mtime={tv_sec=1000, tv_nsec=0} /* 1970-01-01T01:16:40+0100 */,
   stx_rdev_major=0, stx_rdev_minor=0, stx_dev_major=252,
   stx_dev_minor=0, stx_mnt_id=0x1f}) = 0
# but when we statx the file, we get back an mtime of 1000
# but an atime corresponding to when the other process read it

and which will cause the test program to fail with the error
message "stat time".

In theory we could defend against this by e.g.  operating on files in
a dummy loopback mount filesystem which we mounted as 'noatime', but
this isn't worth the hassle.  Just drop the check on atime.

Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20251016150357.876415-4-alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

diff --git a/tests/tcg/multiarch/linux/linux-test.c b/tests/tcg/multiarch/linux/linux-test.c
index 64f57cb287e..bf6e0fda262 100644
--- a/tests/tcg/multiarch/linux/linux-test.c
+++ b/tests/tcg/multiarch/linux/linux-test.c
@@ -155,9 +155,14 @@ static void test_file(void)
         error("stat mode");
     if ((st.st_mode & 0777) != 0600)
         error("stat mode2");
-    if (st.st_atime != 1001 ||
-        st.st_mtime != 1000)
+    /*
+     * Only check mtime, not atime: other processes such as
+     * virus scanners might race with this test program and get
+     * in and update the atime, causing random failures.
+     */
+    if (st.st_mtime != 1000) {
         error("stat time");
+    }
 
     chk_error(stat(tmpdir, &st));
     if (!S_ISDIR(st.st_mode))
-- 
2.47.3