+ userfaultfd-selftests-infinite-loop-in-faulting_process.patch added to mm-unstable branch

+ userfaultfd-selftests-infinite-loop-in-faulting_process.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: userfaultfd: selftests: infinite loop in faulting_process
has been added to the -mm mm-unstable branch.  Its filename is
     userfaultfd-selftests-infinite-loop-in-faulting_process.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/userfaultfd-selftests-infinite-loop-in-faulting_process.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

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------------------------------------------------------
From: Edward Liaw <edliaw@google.com>
Subject: userfaultfd: selftests: infinite loop in faulting_process
Date: Mon, 13 Jun 2022 23:33:21 +0000

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 <edliaw@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/vm/userfaultfd.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/tools/testing/selftests/vm/userfaultfd.c~userfaultfd-selftests-infinite-loop-in-faulting_process
+++ a/tools/testing/selftests/vm/userfaultfd.c
@@ -963,7 +963,7 @@ static int faulting_process(int signal_t
 	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_t
 	}
 
 	for (nr = 0; nr < split_nr_pages; nr++) {
-		int steps = 1;
+		volatile int steps = 1;
 		unsigned long offset = nr * page_size;
 
 		if (signal_test) {
_

Patches currently in -mm which might be from edliaw@google.com are

userfaultfd-selftests-infinite-loop-in-faulting_process.patch