From 4775512dfcd8dcf73089fc4674b1f6307ab415a5 Mon Sep 17 00:00:00 2001 From: Edward Liaw Date: Mon, 13 Jun 2022 23:33:21 +0000 Subject: [PATCH] userfaultfd: selftests: infinite loop in faulting_process On Android this test is getting stuck in an infinite loop due to indeterminate behavior: The local variables steps and signalled were being reset to 1 and 0 respectively after every jump back to sigsetjmp by siglongjmp in the signal handler. The test was incrementing them and expecting them to retain their incremented values. The documentation for siglongjmp says: All accessible objects have values as of the time sigsetjmp() was called, except that the values of objects of automatic storage duration which are local to the function containing the invocation of the corresponding sigsetjmp() which do not have volatile-qualified type and which are changed between the sigsetjmp() invocation and siglongjmp() call are indeterminate. Tagging steps and signalled with volatile enabled the test to pass. Link: https://lkml.kernel.org/r/20220613233321.431282-1-edliaw@google.com Signed-off-by: Edward Liaw Reviewed-by: Axel Rasmussen Cc: Shuah Khan Cc: Peter Xu Signed-off-by: Andrew Morton --- tools/testing/selftests/vm/userfaultfd.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c index 3bba3a54d10d..28b881523d15 100644 --- a/tools/testing/selftests/vm/userfaultfd.c +++ b/tools/testing/selftests/vm/userfaultfd.c @@ -963,7 +963,7 @@ static int faulting_process(int signal_test) unsigned long split_nr_pages; unsigned long lastnr; struct sigaction act; - unsigned long signalled = 0; + volatile unsigned long signalled = 0; split_nr_pages = (nr_pages + 1) / 2; @@ -978,7 +978,7 @@ static int faulting_process(int signal_test) } for (nr = 0; nr < split_nr_pages; nr++) { - int steps = 1; + volatile int steps = 1; unsigned long offset = nr * page_size; if (signal_test) { -- 2.51.0