UML - Definitively kill subprocesses on panic
PATCH 3/3 UML - Definitively kill subprocesses on panic
From: Lepton Wu <[email protected]>
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 ]
--- arch/um/os-Linux/skas/process.c | 2 +- arch/um/os-Linux/util.c | 38 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 39 insertions(+), 1 deletion(-)
arch/um/os-Linux/util.c +38 -0
@@ -105,6 +105,44 @@ int setjmp_wrapper(void (*proc)(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 (); }
arch/um/os-Linux/skas/process.c +1 -1
@@ -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",
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