uml: definitively kill subprocesses on panic

In a stock 2.6.22.6 kernel, poweroff a user mode linux guest (2.6.22.6 running
in skas0 mode) will halt the host linux.  I think the reason is the kernel
thread abort because of a bug.  Then the sys_reboot in process of user mode
linux guest is not trapped by the user mode linux kernel and is executed by
host.  I think it is better to make sure all of our children process to quit
when user mode linux kernel abort.

[ jdike - the kernel process needs to ignore SIGTERM, plus the waitpid/kill
loop is needed to make sure that all of our children are dead before the
kernel exits ]

Signed-off-by: Lepton Wu <ytht.net@gmail.com>
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>

diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index e60d6e6c5a58a913c0abbce0f0d8b78c01857afb..d77c81d7068a06309ecf935ee0ccb9938d4cd8b6 100644 (file)
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -177,7 +177,7 @@ static int userspace_tramp(void *stack)
 
        ptrace(PTRACE_TRACEME, 0, 0, 0);
 
-       init_new_thread_signals();
+       signal(SIGTERM, SIG_DFL);
        err = set_interval();
        if (err)
                panic("userspace_tramp - setting timer failed, errno = %d\n",

diff --git a/arch/um/os-Linux/util.c b/arch/um/os-Linux/util.c
index 7cbcf484e13d3337d8bbaaa06d3fed165a02f377..ef095436a78c24f669dfc54d1ef8af9eb376687d 100644 (file)
--- a/arch/um/os-Linux/util.c
+++ b/arch/um/os-Linux/util.c
@@ -105,6 +105,44 @@ int setjmp_wrapper(void (*proc)(void *, void *), ...)
 
 void os_dump_core(void)
 {
+       int pid;
+
        signal(SIGSEGV, SIG_DFL);
+
+       /*
+        * We are about to SIGTERM this entire process group to ensure that
+        * nothing is around to run after the kernel exits.  The
+        * kernel wants to abort, not die through SIGTERM, so we
+        * ignore it here.
+        */
+
+       signal(SIGTERM, SIG_IGN);
+       kill(0, SIGTERM);
+       /*
+        * Most of the other processes associated with this UML are
+        * likely sTopped, so give them a SIGCONT so they see the
+        * SIGTERM.
+        */
+       kill(0, SIGCONT);
+
+       /*
+        * Now, having sent signals to everyone but us, make sure they
+        * die by ptrace.  Processes can survive what's been done to
+        * them so far - the mechanism I understand is receiving a
+        * SIGSEGV and segfaulting immediately upon return.  There is
+        * always a SIGSEGV pending, and (I'm guessing) signals are
+        * processed in numeric order so the SIGTERM (signal 15 vs
+        * SIGSEGV being signal 11) is never handled.
+        *
+        * Run a waitpid loop until we get some kind of error.
+        * Hopefully, it's ECHILD, but there's not a lot we can do if
+        * it's something else.  Tell os_kill_ptraced_process not to
+        * wait for the child to report its death because there's
+        * nothing reasonable to do if that fails.
+        */
+
+       while ((pid = waitpid(-1, NULL, WNOHANG)) > 0)
+               os_kill_ptraced_process(pid, 0);
+
        abort();
 }