uml: work around broken host PTRACE_SYSEMU

Fedora broke PTRACE_SYSEMU again, and UML crashes as a result when it
doesn't need to.  This patch makes the PTRACE_SYSEMU check fail gracefully
and makes UML fall back to PTRACE_SYSCALL.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 9 deletions

diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index b4b36e0f2e89..183db26d01bf 100644
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -121,8 +121,10 @@ static int stop_ptraced_child(int pid, int exitcode, int mustexit)
 {
         int status, n, ret = 0;
 
-        if (ptrace(PTRACE_CONT, pid, 0, 0) < 0)
-                fatal_perror("stop_ptraced_child : ptrace failed");
+        if (ptrace(PTRACE_CONT, pid, 0, 0) < 0) {
+                perror("stop_ptraced_child : ptrace failed");
+                return -1;
+        }
         CATCH_EINTR(n = waitpid(pid, &status, 0));
         if (!WIFEXITED(status) || (WEXITSTATUS(status) != exitcode)) {
                 int exit_with = WEXITSTATUS(status);
@@ -212,7 +214,7 @@ static void __init check_sysemu(void)
         if (n < 0)
                 fatal_perror("check_sysemu : wait failed");
         if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGTRAP))
-                fatal("check_sysemu : expected SIGTRAP, got status = %d",
+                fatal("check_sysemu : expected SIGTRAP, got status = %d\n",
                       status);
 
         if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
@@ -254,9 +256,11 @@ static void __init check_sysemu(void)
 
                 if (WIFSTOPPED(status) &&
                     (WSTOPSIG(status) == (SIGTRAP|0x80))) {
-                        if (!count)
-                                fatal("check_ptrace : SYSEMU_SINGLESTEP "
-                                      "doesn't singlestep");
+                        if (!count) {
+                                non_fatal("check_ptrace : SYSEMU_SINGLESTEP "
+                                          "doesn't singlestep");
+                                goto fail;
+                        }
                         n = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_RET_OFFSET,
                                    os_getpid());
                         if (n < 0)
@@ -266,9 +270,12 @@ static void __init check_sysemu(void)
                 }
                 else if (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGTRAP))
                         count++;
-                else
-                        fatal("check_ptrace : expected SIGTRAP or "
-                              "(SIGTRAP | 0x80), got status = %d", status);
+                else {
+                        non_fatal("check_ptrace : expected SIGTRAP or "
+                                  "(SIGTRAP | 0x80), got status = %d\n",
+                                  status);
+                        goto fail;
+                }
         }
         if (stop_ptraced_child(pid, 0, 0) < 0)
                 goto fail_stopped;