The patch titled Subject: signal: kill the obsolete SIGNAL_UNKILLABLE check in complete_signal() has been added to the -mm tree. Its filename is signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Oleg Nesterov <oleg@xxxxxxxxxx> Subject: signal: kill the obsolete SIGNAL_UNKILLABLE check in complete_signal() complete_signal() checks SIGNAL_UNKILLABLE before it starts to destroy the thread group, today this is unnecessary and even not 100% correct. After the commit f008faff0e27 ("signals: protect init from unwanted signals more") we rely on sig_task_ignored(), complete_signal(SIGKILL) can only see a SIGNAL_UNKILLABLE task if we actually want to kill it. And note that after the commit b3bfa0cba867 ("signals: protect cinit from blocked fatal signals") we do not drop SIGKILL dequeued by /sbin/init. And it does not look right. fatal_signal_pending() should always imply that the whole thread group (except ->group_exit_task if it is not NULL) is killed, this check breaks the rule. This explains WARN_ON(!JOBCTL_STOP_PENDING) in task_participate_group_stop() triggered by the test-case from Dmitry: int main() { int pid = 1; ptrace(PTRACE_ATTACH, pid, 0, 0); ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_EXITKILL); sleep(1); return 0; } do_signal_stop()->signal_group_exit() returns false because SIGNAL_GROUP_EXIT is not set, but task_set_jobctl_pending() checks fatal_signal_pending() and does not set JOBCTL_STOP_PENDING. The test-case above needs root and (correctly) crashes the kernel, but we can trigger the same warning inside the container or using another test-case: static int init(void *arg) { for (;;) pause(); } int main(void) { char stack[16 * 1024]; for (;;) { int pid = clone(init, stack + sizeof(stack)/2, CLONE_NEWPID | SIGCHLD, NULL); assert(pid > 0); assert(ptrace(PTRACE_ATTACH, pid, 0, 0) == 0); assert(waitpid(-1, NULL, WSTOPPED) == pid); assert(ptrace(PTRACE_DETACH, pid, 0, SIGSTOP) == 0); assert(syscall(__NR_tkill, pid, SIGKILL) == 0); assert(pid == wait(NULL)); } } Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/signal.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN kernel/signal.c~signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal kernel/signal.c --- a/kernel/signal.c~signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal +++ a/kernel/signal.c @@ -909,7 +909,7 @@ static void complete_signal(int sig, str * then start taking the whole group down immediately. */ if (sig_fatal(p, sig) && - !(signal->flags & (SIGNAL_UNKILLABLE | SIGNAL_GROUP_EXIT)) && + !(signal->flags & SIGNAL_GROUP_EXIT) && !sigismember(&t->real_blocked, sig) && (sig == SIGKILL || !t->ptrace)) { /* _ Patches currently in -mm which might be from oleg@xxxxxxxxxx are mmoom-fix-potentially-killing-unrelated-process-fix.patch mm-fix-the-racy-mm-locked_vm-change-in.patch mm-add-the-struct-mm_struct-mm-local-into.patch mm-oom_kill-remove-the-wrong-fatal_signal_pending-check-in-oom_kill_process.patch mm-oom_kill-cleanup-the-kill-sharing-same-memory-loop.patch mm-oom_kill-fix-the-wrong-task-mm-==-mm-checks-in-oom_kill_process.patch proc-actually-make-proc_fd_permission-thread-friendly.patch change-current_is_single_threaded-to-use-for_each_thread.patch signals-kill-block_all_signals-and-unblock_all_signals.patch signal-turn-dequeue_signal_lock-into-kernel_dequeue_signal.patch signal-turn-dequeue_signal_lock-into-kernel_dequeue_signal-fix.patch signal-introduce-kernel_signal_stop-to-fix-jffs2_garbage_collect_thread.patch signal-remove-jffs2_garbage_collect_thread-allow_signalsigcont.patch signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal.patch coredump-ensure-all-coredumping-tasks-have-signal_group_coredump.patch coredump-change-zap_threads-and-zap_process-to-use-for_each_thread.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html