linux-kernel - [PATCH] proc: hide "segfault at ffffffffff600000" dmesg spam

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Message-ID: <20190524181256.GA2260@avx2>
Date:   Fri, 24 May 2019 21:12:56 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] proc: hide "segfault at ffffffffff600000" dmesg spam

Test tries to access vsyscall page and if it doesn't exist gets SIGSEGV
which can spam into dmesg. However the segfault happens by design.
Handle it and carry information via exit code to parent.

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 tools/testing/selftests/proc/proc-pid-vm.c |   17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

--- a/tools/testing/selftests/proc/proc-pid-vm.c
+++ b/tools/testing/selftests/proc/proc-pid-vm.c
@@ -215,6 +215,11 @@ static const char str_vsyscall[] =
 "ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]\n";
 
 #ifdef __x86_64__
+static void sigaction_SIGSEGV(int _, siginfo_t *__, void *___)
+{
+	_exit(1);
+}
+
 /*
  * vsyscall page can't be unmapped, probe it with memory load.
  */
@@ -231,11 +236,19 @@ static void vsyscall(void)
 	if (pid == 0) {
 		struct rlimit rlim = {0, 0};
 		(void)setrlimit(RLIMIT_CORE, &rlim);
+
+		/* Hide "segfault at ffffffffff600000" messages. */
+		struct sigaction act;
+		memset(&act, 0, sizeof(struct sigaction));
+		act.sa_flags = SA_SIGINFO;
+		act.sa_sigaction = sigaction_SIGSEGV;
+		(void)sigaction(SIGSEGV, &act, NULL);
+
 		*(volatile int *)0xffffffffff600000UL;
 		exit(0);
 	}
-	wait(&wstatus);
-	if (WIFEXITED(wstatus)) {
+	waitpid(pid, &wstatus, 0);
+	if (WIFEXITED(wstatus) && WEXITSTATUS(wstatus) == 0) {
 		g_vsyscall = true;
 	}
 }