selftests/sigaltstack: Fix the sigaltstack test on old kernels

The handling for old kernels was wrong, resulting in a segfault.  Fix it.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Stas Sergeev <stsp@list.ru>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-api@vger.kernel.org
Link: http://lkml.kernel.org/r/f3e739bf435beeaecbd5f038f1359d2eac6d1e63.1462296606.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 14 insertions, 7 deletions

diff --git a/tools/testing/selftests/sigaltstack/sas.c b/tools/testing/selftests/sigaltstack/sas.c
index 57da8bfde60b..a98c3ef8141f 100644
--- a/tools/testing/selftests/sigaltstack/sas.c
+++ b/tools/testing/selftests/sigaltstack/sas.c
@@ -15,6 +15,7 @@
 #include <alloca.h>
 #include <string.h>
 #include <assert.h>
+#include <errno.h>
 
 #ifndef SS_AUTODISARM
 #define SS_AUTODISARM  (1 << 4)
@@ -117,13 +118,19 @@ int main(void)
         stk.ss_flags = SS_ONSTACK | SS_AUTODISARM;
         err = sigaltstack(&stk, NULL);
         if (err) {
-                perror("[FAIL]\tsigaltstack(SS_ONSTACK | SS_AUTODISARM)");
-                stk.ss_flags = SS_ONSTACK;
-        }
-        err = sigaltstack(&stk, NULL);
-        if (err) {
-                perror("[FAIL]\tsigaltstack(SS_ONSTACK)");
-                return EXIT_FAILURE;
+                if (errno == EINVAL) {
+                        printf("[NOTE]\tThe running kernel doesn't support SS_AUTODISARM\n");
+                        /*
+                         * If test cases for the !SS_AUTODISARM variant were
+                         * added, we could still run them.  We don't have any
+                         * test cases like that yet, so just exit and report
+                         * success.
+                         */
+                        return 0;
+                } else {
+                        perror("[FAIL]\tsigaltstack(SS_ONSTACK | SS_AUTODISARM)");
+                        return EXIT_FAILURE;
+                }
         }
 
         ustack = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,