um: fix abort

os_dump_core() uses abort() to terminate UML in case of an fatal error.

glibc's abort() calls raise(SIGABRT) which makes use of tgkill().
tgkill() has no effect within UML's kernel threads because they are not
pthreads.  As fallback abort() executes an invalid instruction to
terminate the process.  Therefore UML gets killed by SIGSEGV and leaves a
ugly log entry in the host's kernel ring buffer.

To get rid of this we use our own abort routine.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/um/os-Linux/util.c b/arch/um/os-Linux/util.c
index 6ea77979531c95e1bf005eb0cc3e4a87fa6c913d..42827cafa6af3ac72f4c57d62e08968b81360faa 100644 (file)
--- a/arch/um/os-Linux/util.c
+++ b/arch/um/os-Linux/util.c
@@ -5,6 +5,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 #include <errno.h>
 #include <signal.h>
 #include <string.h>
@@ -75,6 +76,26 @@ void setup_hostinfo(char *buf, int len)
                 host.release, host.version, host.machine);
 }
 
+/*
+ * We cannot use glibc's abort(). It makes use of tgkill() which
+ * has no effect within UML's kernel threads.
+ * After that glibc would execute an invalid instruction to kill
+ * the calling process and UML crashes with SIGSEGV.
+ */
+static inline void __attribute__ ((noreturn)) uml_abort(void)
+{
+       sigset_t sig;
+
+       fflush(NULL);
+
+       if (!sigemptyset(&sig) && !sigaddset(&sig, SIGABRT))
+               sigprocmask(SIG_UNBLOCK, &sig, 0);
+
+       for (;;)
+               if (kill(getpid(), SIGABRT) < 0)
+                       exit(127);
+}
+
 void os_dump_core(void)
 {
        int pid;
@@ -116,5 +137,5 @@ void os_dump_core(void)
        while ((pid = waitpid(-1, NULL, WNOHANG | __WALL)) > 0)
                os_kill_ptraced_process(pid, 0);
 
-       abort();
+       uml_abort();
 }